Many people believe that a secure investment is to hold the bitcoins. No, bitcoins is money. Like as fiat money his price has up and down. Bitcoin's drawback till now is the big volatility compared to fiat money. This may be change in near future as the maturity of bitcoin increases over the time. Investments is the same as fiat too. Instead of deposit fiat you deposit coins. The same with withdrawal.
Though if technically we see just holding money is not called an investment, but in bitcoin the case is different as the money you hold in bitcoin grows with the time and we know technically we invest money only in order to get more money out of that and bitcoin does that for us if we just hold it.