The best I have found is Chipstars, but again it converts to fiat to bet with.
OP is looking for a casino where when he deposits in bitcoin he can withdraw 1 bitcoin when he wants to withdraw, even if he wins and keeps 2 bitcoin and the price of bitcoin drops a lot OP could still withdraw 2 BTC, OP wants casino that does not convert crypto to fiat, I gave an example of the stake that they didn't convert to, I don't know if I'm not wrong, because when the person puts it to see the balance in FIAT, every time the price of the currency fluctuates, the person realizes that the balance is rising or falling
but when the balance is in cryptocurrency I see it and even when market prices go up or down the balance remains the same, I could be wrong about that
You can keep your balance is USDT at Betcoin.