Investing.com - Wall Street's biggest bull on cryptocurrencies isn't losing faith.Even with 2018's brutal selloff, Fundstrat Global Advisors head of research Tom Lee still expects big things this year.In a note to clients, Lee said selloffs of such magnitude in the past were followed by huge recoveries, which means investors should be buying at this time even if there is the risk of additional declines.The recent selloff has knocked half the value off of Bitcoin, which was at a record high of almost 19,000 in December.Lee still expects bitcoin to hit $20,000 by mid-year and $25,000 by year end. Lee predicts the price of Ethereum, currently the number two cryptocurrency based on market capitalization, to reach $1,900 by year end. Lee believes that millennial investors will help cryptocurrencies gain traction and broader acceptance.A recent survey showed that 30% of millennials would rather invest in bitcoin than stocks or government bonds.