Corporate insiders sell their own companies' stock for a number of reasons. ¿

They might need the cash for a big personal purchase such as a new house or yacht, or they might need the cash to fund a charity. Sometimes they sell as part of a planned selling program that they have put in place for diversification purposes, which allows them to sell stock in stages instead of selling all at one price.

Other times they sell because they think their stock is overvalued and the risk/reward is no longer attractive. Some even dump their own stock because they have inside knowledge that a competitor is eating their lunch and stealing market share. ¿

But insiders usually buy their own shares for one reason: They think the stock is a bargain and has tremendous upside.

The key word in that last statement is "think." Just because a corporate insider thinks his or her stock is going to trade higher, that doesn't mean it will play out that way. Insiders can have all the conviction in the world that their stock is a buy, but if the market doesn't agree with them, the stock could end up going nowhere. Also, I say "usually" because sometimes insiders are loaned money by the company to buy their own stock. Those loans are often sweetheart deals and shouldn't be viewed as organic insider buying.

At the end of the day, it's institutional money managers running big mutual funds and hedge funds that drive stock prices, not insiders. That said, many of these savvy stock operators will follow insider buying activity when they agree with the insider that the stock is undervalued and has upside potential. This is why it's so important to always be monitoring insider activity but twice as important to make sure the trend of the stock coincides with the insider buying.

Recently, a number of companies' corporate insiders have bought large amounts of stock. These insiders are finding some value in the market, which warrants a closer look at these stocks.

Freshpet

One consumer goods player that insiders are in love with here is Freshpet(FRPT) - Get Report, which manufactures and markets natural fresh foods, refrigerated meals and treats for dogs and cats in the U.S. and Canada. Insiders are buying this stock into major weakness, since shares have plunged by 62% over the last six months.

Freshpet has a market cap of $251 million and an enterprise value of $198 million. This stock trades at a premium valuation, with a forward price-to-earnings of 375. Its estimated growth rate for this year is 72.7%, and for next year it's pegged at 109.5%. This is a cash-rich company, since the total cash position on its balance sheet is $19 million and its total debt is zero.

A beneficial owner just bought 343,820 shares, or about $2.18 million worth of stock, at $6.26 to $6.85 per share.

From a technical perspective, Freshpet is currently trending below both its 50-day and 200-day moving averages, which is bearish. This stock has been uptrending over the last few weeks, with shares moving notably higher off its low of $5.89 to its intraday high on Tuesday of $7.64 a share. During that uptrend, shares of Freshpet have been consistently making higher lows and higher highs, which is bullish technical price action.

If you're bullish on Freshpet, then I would look for long-biased trades as long as this stock is trending above some near-term support at around $7 a share and then once it breaks out above Tuesday's intraday high of $7.64 to its 20-day moving average of $8.08 a share with high volume. Look for a sustained move or close above those levels with volume that hits near or above its three-month average action of 598,531 shares. If that breakout gets set off soon, then this stock will set up to re-test or possibly take out its next major overhead resistance levels at $9 to its 50-day moving average of $9.43 a share.

YuMe

Another advertising player that insider are jumping into here is YuMe (YUME) , which provides digital video brand advertising solutions in the U.S. and internationally. Insiders are buying this stock into large weakness, since shares have dropped sharply by 38.2% over the last six months.

YuMe has a market cap of $108.4 million and an enterprise value of $57.9 million. This stock trades at a reasonable valuation, with a price-to-sales of 0.60 and a price-to-book of 1.08. Its estimated growth rate for this year is -64.7%, and for next year it's pegged at 60.7%. This is a cash-rich company, since the total cash position on its balance sheet is $48.46 million and its total debt is zero.

A beneficial owner just bought 782,841 shares, or about $2.08 million worth of stock, at $2.66 to $2.70 per share.

From a technical perspective, YuMe is currently trending above its 50-day moving average and well below its 200-day moving average, which is neutral trendwise. This stock has been uptrending over the last few weeks, with shares moving higher from its low of $2.59 to its intraday high on Tuesday of $3.15 a share. During that uptrend, shares of YuMe have been consistently making higher lows and higher highs, which is bullish technical price action. This move has now pushed this stock within range of triggering a near-term breakout trade above some key overhead resistance levels.

If you're in the bull camp on YuMe, then I would look for long-biased trades as long as this stock is trending above its 50-day moving average of $2.92 a share and then once it breaks out above some near-term overhead resistance levels at $3.25 to $3.30 a share with volume that registers near or above its three-month average action of 217,454 shares. If that breakout develops soon, then this stock will set up to re-test or possibly take out its next major overhead resistance levels at $3.50 to around its gap-down-day high from August near $4 a share. Any high-volume move above those levels will then give this stock a chance to re-fill some of its previous gap-down-day zone that started near $4.75 a share.

Plains GP Holdings

One energy player that insiders are active in here is Plains GP Holdings(PAGP) - Get Report , which owns and operates midstream energy infrastructure and provides logistics services for crude oil, natural gas liquids, natural gas and refined products in the U.S. and Canada. Insiders are buying this stock into big weakness, since shares have fallen sharply by 59.7% over the last six months.

Plains GP Holdings has a market cap of $2.6 billion and an enterprise value of $13.7 billion. This stock trades at a reasonable valuation, with a trailing price-to-earnings of 23.4 and a forward price-to-earnings of 15.2. Its estimated growth rate for this year is 34%, and for next year it's pegged at 20.6%. This is not a cash-rich company, since the total cash position on its balance sheet is $25 million and its total debt is $11.27 billion. This stock currently sports a dividend yield of 8.6%.

The CEO just bought 100,000 shares, or about $1.10 million worth of stock, at $11.09 per share.

From a technical perspective, Plains GP Holdings is currently trending below both its 50-day and 200-day moving averages, which is bearish. This stock recently has been downtrending badly over the last two months, with shares falling sharply lower from its high of $19.21 to its new 52-week low of $10.41 a share. During that downtrend, shares of Plains GP Holdings have been consistently making lower highs and lower lows, which is bearish technical price action. That said, this stock has now started to spike higher off that $10.41 low and it's beginning to trend within range of triggering a major breakout trade above some key near-term overhead resistance levels.

If you're bullish on Plains GP Holdings, then I would look for long-biased trades as long as this stock is trending above its new 52-week low of $10.41 a share and then once it breaks out above some near-term overhead resistance levels at $12.59 to its 20-day moving average of $12.86 and then above more resistance at $13 a share with high volume. Look for a sustained move or close above those levels with volume that registers near or above its three-month average volume of 2.84 million shares. If that breakout fires off soon, then this stock will set up to re-test or possibly take out its next major overhead resistance levels at $15 to its 50-day moving average of $15.86, or even $16.34 to $17 a share.

Gap

One apparel retail player that insiders are snapping up a decent amount of stock in here is Gap(GPS) - Get Report , which offers apparel, accessories, and personal care products for men, women and children under the Gap, Banana Republic, Old Navy, Athleta and Intermix brand names. Insiders are buying this stock into notable weakness, since shares have dropped by 26.8% over the last six months.

The Gap has a market cap of $11.2 billion and an enterprise value of $11.6 billion. This stock trades at a fair valuation, with a trailing price-to-earnings of 11.3 and a forward price-to-earnings of 10.9. Its estimated growth rate for this year -14.9%, and for next year it's pegged at 5.8%. This is not a cash-rich company, since the total cash position on its balance sheet is $1.04 billion and its total debt is $1.75 billion. This stock currently sports a dividend yield of 3.4%.

The CEO just bought 37,150 shares, or about $1 million worth of stock, at $26.99 per share.

From a technical perspective, Gap is currently trending below both its 50-day and 200-day moving averages, which is bearish. This stock has been uptrending over the last few weeks, with shares moving higher from its low of $24.70 to its intraday high on Tuesday of $27.86 a share. During that uptrend, shares of Gap have been making mostly higher lows and higher highs, which is bullish technical price action. That move has now pushed this stock within range of triggering a near-term breakout trade above some key overhead resistance levels.

If you're bullish on Gap, then I would look for long-biased trades as long as this stock is trending above its 20-day moving average of $26.88 or above more near-term support at $26 a share and then once it breaks out above some near-term overhead resistance levels at its 50-day moving average of $27.81 a share and then above more key resistance levels at $28.65 to $29.19 a share with high volume. Look for a sustained move or close above those levels with volume that hits near or above its three-month average action of 5.60 million shares. If that breakout develops soon, then this stock will set up to re-test or possibly take out its next major overhead resistance levels at $31 to $32, or even $33 to its 200-day moving average of $35.40 a share.

Scientific Games

One final stock with some big insider buying is gaming player Scientific Games(SGMS) - Get Report , which develops technology-based products and services and associated content for the gaming and lottery industries worldwide. Insiders are buying this stock into large weakness, since shares have dropped by 42.1% over the last six months.

Scientific Games has a market cap of $746 million and an enterprise value of $9.05 billion. This stock trades at a reasonable valuation, with a price-to-sales of 0.28. Its estimated growth rate for this year is -301.8%, and for next year it's pegged at 63.1%. This is not a cash-rich company, since the total cash position on its balance sheet is $102.10 million and its total debt is $8.42 billion.

A director just bought 300,000 shares, or about $2.4 million worth of stock, at $7.80 per share. From a technical perspective, Scientific Games is currently trending below both its 50-day and 200-day moving averages, which is bearish. This stock recently gapped-down sharply lower from over $12 a share to under $9 a share with heavy downside volume flows. This stock went on to print a new 52-week low of $7.51 a share following that gap to the downside. Shares of Scientific Games have now started to rebound higher off that $7.51 low and it's beginning to trend within range of triggering a major breakout trade above some key near-term overhead resistance levels.

If you're bullish on Scientific Games, then I would look for long-biased trades as long as this stock is trending above some near-term support at $8.19 a share or above $8 a share and then once it breaks out above some near-term overhead resistance at $9 a share with high volume. Look for a sustained move or close above that level with volume that hits near or above its three-month average volume of 1.15 million shares. If that breakout takes hold soon, then this stock will set up to re-test or possibly take out its next major overhead resistance levels at $10 a share. Any high-volume move above $10 a share will then give this stock a chance to re-fill some of its previous gap-down-day zone from a few weeks ago that started near $12 a share.

Disclosure: This article is commentary by an independent contributor. At the time of publication, the author held no positions in the stocks mentioned.