二叉树的基本操作。包括树的（先序、中序、后序）创建、树的遍历（先序、中序、后序）、树的高度、树的宽度、树的叶子节点数-The basic operation of a binary tree. Including tree (first order, in sequence after sequence) created tree traversal (first order, in sequence after sequence), tree height, tree width, tree