def get_from_subtree(subtree, key):
    """
    Find the value associated to the key in the given subtree
    :param subtree: the subtree to search in
    :param key: the key to search for
    :return: the value associated to the key in the given subtree or None if this key is not in the subtree
    """
    temp_subtree = subtree
    while temp_subtree is not None:
        if key == temp_subtree.key:
            return temp_subtree.value
        elif key < temp_subtree.key:
            temp_subtree = temp_subtree.left
        elif key > temp_subtree.key:
            temp_subtree = temp_subtree.right
    return None