This "index fund" is made out of four currencies, BTC, ETH, LTC, BTC cash. Just buy a bunch of those and you're "investing" in their "index". Also you don't have to pay their fee for their immense expertise in putting this together.
0. Average 52-week premium 56.18% https://www.bloomberg.com/quote/GBTC:US
Edit: Apparently they only rebalance once a year? In which case, nvm.