Investing in fixed deposits of banks are generally considered secure and low risk option, because interest is guaranteed, however the amount of interests paid on such deposits  is relatively low and doesn't fully cover the rate of inflation most of the time. On the other hand, investment in bitcoin is high risk and volatile option but potentially it can yield high returns on long term holdings. It is generally advised to exercised this option after fully understanding the fundamentals of Bitcoin technology and dynamics of its market, as well as keeping in view your financial situation and risk tolerance limits.