When you say invest in Bitcoins do you mean just buying them and keeping them or is there a way to buy shares in them?
There's no such thing as shares of bitcoin, and anyone selling "shares in bitcoin" is a scammer. 
Buy them and hold them.
Ok so it is possible to buy shares in the growth of Bitcoin if you believe they will go up in price? There is a share called BTC-GROWTH under the FUND tab on BTC-TC, is this a share for Bitcoin if it increases its value in the future? eg if Bitcoin is worth $200 in the future would you make money if you bought shares now?