Small caps are outperforming the S&P 500 this year, and 'Shark Tank's' Kevin O'Leary is betting on more gains to come

The iShares Russell 2000 ETF (IWM) IWM , which tracks the small cap-focused Russell, has rallied more than 11 percent in 2019, capping off Friday with its third up week in a row. Kevin O'Leary , co-founder of O'Leary Funds and co-host of "Shark Tank," told CNBC recently that several tailwinds should continue to benefit small caps over large caps this year. "Tax reforms haven't had their full effect yet and because the tax code has just been re-written for these all domestic companies.