Standard financial theory says that in the absence of specialized information about what assets are better than others, you want to invest in every single investable asset proportionally to their total value. The Bitcoin market is worth about $2 billion at current prices, compared to some $25 trillion for stocks, meaning that in principle you should put $1 into Bitcoin for every $12,500 you have in stocks. (In practice, transaction costs make this completely infeasible, as should be obvious, but that's the mathematical argument)