Company insiders will sell their own stock for a ton of different reasons. They might need the cash for that new Lamborghini, or they might need the money to pay a large tax bill. Sometimes they sell simply for diversification purposes.

Insiders, however, usually buy their own shares for one reason only: They think the stock is cheap and has tremendous upside.

Recently, a number of companies' corporate insiders have been loading up on their own stock. These insiders smell opportunity, which warrants a closer look at these names.

Audentes Therapeutics

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One biotechnology player that insiders are loading up on here is Audentes Therapeutics(BOLD) - Get Report , which focuses on developing and commercializing gene therapy products for patients suffering from diseases caused by single gene defects in the U.S.

Audentes Therapeutics has a market cap of $403 million. This stock trades at a reasonable valuation, with a price-to-book of 2.73. Its estimated growth rate for this year is 35.1%, and for next year it's pegged at 6.9%.

A beneficial owner bought 172,413 shares, or $2.49 million worth of stock, at $14.50 per share.

If you're bullish on Audentes Therapeutics, then I would look for long-biased trades as long as this stock is trending above some near-term support levels at $14.50 or $14 and then once it breaks out above its 20-day at $15.28 and its 50-day at $15.63 and over $15.70 with volume near or above its three-month average of 111,421 shares. Some possible upside targets off that breakout are $16.45 to $17, or even $18 a share.

Twitter

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Another social media player that insiders are in love with here is Twitter(TWTR) - Get Report , which operates as a global platform for public self-expression and conversation in real time.

Twitter has a market cap of $13.5 billion. This stock trades at a premium valuation, with a forward price-to-earnings of 47.9. Its estimated growth rate for this year is -42.1%, and for next year it's pegged at 18.2%.

The CEO just bought 574,002 shares, or $9.54 million worth of stock, at $16.62 per share.

If you're bullish on Twitter, I would look for long-biased trades if this stock is trending above its 200-day at $17.53 and then once it breaks out above some key resistance levels at $19 to $19.84 with volume near or above its three-month average of 20.74 million shares. Some possible upside targets off that breakout are $21 to $23, or even its 52-week high of $25.25 a share.

Radius Health

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One biopharmaceutical player insiders are jumping into here is Radius Health(RDUS) - Get Report , which develops and sells therapeutics in the areas of osteoporosis, oncology and endocrine diseases primarily in the U.S.

Radius Health has a market cap of $1.59 billion. This stock trades at a fair valuation, with a price-to-book of 5.16. Its estimated growth rate for this year is -1.9%, and for next year it's pegged at 20.8%.

A beneficial owner just bought 150,000 shares, or $5.30 million worth of stock, at $35.39 per share. That same beneficial owner also just bought 75,000 shares, or $2.54 million worth of stock, at $33.91 per share.

If you're in the bull camp on Radius Health, I would look for long-biased trades if this stock is trending above some near-term support levels at $35 to $34 and once it breaks out its 50-day at $38.82 and then above more resistance at $40 with volume near or above its three-month average of 921,063 shares. Some possible upside targets off that breakout are $43.30 to its 200-day at $46.13, or even $48.50 a share.

Biogen

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One biopharmaceutical player that insiders are active in here is Biogen(BIIB) - Get Report , which discovers, develops, manufactures and delivers therapies for the treatment of neurological and autoimmune diseases worldwide.

Biogen has a market cap of $57.6 billion. This stock trades at a reasonable valuation, with a forward price-to-earnings of 11.9. Its estimated growth rate for this year is 1.3%, and for next year it's pegged at 10.2%.

A director just bought 73,858 shares, or $20.56 million worth of stock, at $278.48 per share.

If you're bullish on Biogen, I would look for long-biased trades if this stock is trending above some near-term support levels at $267.10 to $266 and then once it breaks out above its 20-day at $272.77 with volume near or above its three-month average of 1.62 million shares. Some possible upside targets off that breakout are its 200-day at $276.03 to its 50-day at $278.91, or even $285 to $292 a share.

Bank of America

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My final stock with some notable insider buying Bank of America(BAC) - Get Report , which provides banking and financial products and services for individual consumers, small and middle-market businesses, institutional investors, large corporations and governments worldwide.

Bank of America has a market cap of $237.8 billion. This stock trades at a reasonable valuation, with a forward price-to-earnings of 11.14. Its estimated growth rate for this year is 22%, and for next year it's pegged at 16.9%.

A director just bought 25,000 shares, or $595,000 worth of stock, at $23.81 per share.

If you're bullish on Bank of America, I would look for long-biased trades if this stock is trending above its 20-day at $23.2 or above more support at $22.26 and then once it breaks out above some near-term resistance levels at $24.35 to $24.50 with volume near or above its three-month average of 96.97 million shares. If that breakout fires off soon ,then this stock will set up to re-test or possibly take out its next major resistance level at its 52-week high of $25.80 a share.

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