Bitcoin is neither issued by government/bank like fiat nor it is a form of credit to us so there is no need of collateral at all.
Bitcoin hold value based on people's trust over it and supply/demand of bitcoin drives the price. With growing demand and limited supply of bitcoin price is moving upwards if we look at long term charts.

Many experts that's why suggest to only invest what you can loss in bitcoin because it can be worthless in future which is quite unlikely scenario but its better not to take risk with all of your money.