When you deposit money in a bank, it is held as collateral and you can withdraw it whenever you want without any loss. And after a certain period of time the bank gives you interest at a certain percentage rate but in case of Bitcoin your money will never be stable like the bank.
Take note that the fiat currency you hold in banks isn't stable in value.
The bank show you a number as your balance and increase that number as they give you some interest. But this doesn't mean the value of your balance increases. The government prints more money and decreases the real value of your balance.