def backup(self, value_estimate: float):
    current = self
    while current.parent is not None:
        current.number_visits += 1
        if current.game.player == 1: # same as current.parent.game.player = 0
            current.total_value += (1*value_estimate) # value estimate +1 = O wins
        elif current.game.player == 0: # same as current.parent.game.player = 1
            current.total_value += (-1*value_estimate)
        current = current.parent