相关代码：

​public boolean contains(E e){
        if(root == null){
            return false;
        }else {
            return contains(root, e);
        }
    }

    private boolean contains(Node node, E e){
        while(node != null){
            if(e.compareTo(node.e) > 0){
                node = node.right;
            }else if(e.compareTo(node.e) < 0){
                node = node.left;
            }else {
                return true;
            }
        }
        return false;
    }