Member Tree::binaryTree< T, Comparator >::parent (value_type x, const value_type &flag) const: 二叉链表不允许访问结点的parent，本函数恒返回flag
Member Tree::printBinaryTree (const binaryTree< T, Comparator > &bin_tree, const typename binaryTree< T, Comparator >::value_type &flag, std::ostream &out=std::cout): bin_tree中不允许含有data相同的结点，否则可能导致无限循环！