There is no extra cost or commissions charged for trading Bitcoin(BTCUSD) on XM MT5.

The only cost you need to pay is the spread which is 12 at the lowest.

Other than that, in case you hold an open positions of BTCUSD overnight, there will be Swap points occurred at 00:00 in server time. Unfortunately swap points of BTCUSD are often negative, thus you maybe charged for both long and short positions.