应用题-二叉树专题-二叉搜索树中的插入操作
```python
# Definition for a binary tree node.
# class TreeNode:
# def __init__(self, val=0, left=None, right=None):
# self.val = val
# self.left = left
# self.right = right
class Solution:
def insertIntoBST(self, root: Optional[TreeNode], val: int) -> Optional[TreeNode]:
if not root: return TreeNode( val )
# 放在叶子节点 比较简单
r = root
while r:
if not r.left and val < r.val:
r.left = TreeNode( val )
break
if not r.right and val > r.val:
r.right = TreeNode( val )
break
if val > r.val: r = r.right
else: r = r.left
return root
```