Propagates a value estimation up to the root node.

        Args:
            value: the value to be propagated (1 = black wins, -1 = white wins)
            up_to: the node to propagate until.

def backup_value(self, value, up_to):
        """Propagates a value estimation up to the root node.

        Args:
            value: the value to be propagated (1 = black wins, -1 = white wins)
            up_to: the node to propagate until.
        """
        self.N += 1
        self.W += value
        if self.parent is None or self is up_to:
            return
        self.parent.backup_value(value, up_to)