Looking for the adrenaline rush of investing in Bitcoin but without the bother of crypto-exchanges and digital wallets? An exchange-traded fund might do the trick, except an investor won’t find one tracking Bitcoin anywhere in the $6.2 trillion U.S. ETF universe -- at least not yet. While exchange-traded crypto-tracking products exist in Europe and a Bitcoin ETF opened in February in Canada, U.S. regulators have repeatedly batted down attempts to introduce them, citing concerns about potential m