Shark Tank star Kevin O'Leary, chairman of O'Shares ETF Investments, is bullish on mid-cap and small-cap stocks for the rest of 2017.

"The mid-cap small-cap space has not participated in the recent rally even though the dollar has been pummeled," he said. "But you have to remember, small-cap stocks have about 100% of their revenue domestically so they're not as exposed to currency fluctuations and yet their earnings have been healthy and they haven't had their move."

O'Leary said any tax reform plans from the Trump administration will benefit the mid and small-cap space, along with the S&P 500. He's betting on the former for the back end of 2017.

Meanwhile, it's no secret that far too many Americans haven't saved enough money for retirement.

One reason why is because people don't start saving early enough to take advantage of compounding interest.

That's why O'Leary started Beanstox, an app that allows users to invest in fractions of shares of stocks.

O'Leary said those who can't afford a share of Apple (AAPL) may be able to afford a fraction of a share.

Apple is a holding in Jim Cramer's Action Alerts PLUS Charitable Trust Portfolio. Want to be alerted before Cramer and the AAP team buy or sell AAPL? Learn more now.

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