Someone out there just made a bet that bitcoin will surge above $50,000 next year, trading data show—about triple its current price.

Daily trading records released Wednesday by LedgerX, a startup electronic market for bitcoin derivatives, show that an unidentified trader or traders entered the bullish bets using bitcoin call options that expire next December. The trade wagering on a move to $50,000 was the first of its kind on LedgerX.

Just...