binary tree的用法和樣例：
例句
- Write a function to find the depth of a binary tree.
寫(xiě)個(gè)程序找到一個(gè)二叉樹(shù)的深度。 - If a binary tree becomes degenerate, we run into the same efficiency problems as we did with the singly linked list.
如果二叉樹(shù)變得很不平衡，我們將會(huì )碰到同樣的效率問(wèn)題如同在持久化單向鏈表是一樣。
