Leetcode: Convert Sorted Array to Binary Search Tree @Python

# Definition for a  binary tree node
# class TreeNode:
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None

class Solution:
    # @param num, a list of integers
    # @return a tree node
    def sortedArrayToBST(self, num):
        n=len(num)
        if n==0: return None
        mid=n//2
        root=TreeNode(num[mid])
        root.left=self.sortedArrayToBST(num[:mid])
        root.right=self.sortedArrayToBST(num[mid+1:])
        return root