数据结构树的演示程序，包括等价类合并、二叉树基本操作的实现、哈夫曼树、线索二叉树、前、中缀二叉树、表达式求值等程序。- The tree data structure demo program, including the equivalence class combination, two tree basic operations to achieve Huffman tree, binary tree, two clues, and two binary tree, infix