Python – A recursive solution to Symmetirc Tree

I tried to solve a symmetric tree problem

Given a binary tree, check if it is a mirror of itself (ie, symmetric around its center).

For example, this binary tree. [1,2,2,3,4,4,3] it's symmetrical

2 2
/  / 
3 4 4 3

But the following [1,2,2,null,3,null,3] It is not:

2 2
3 3

Bonus points if I could solve them recursively and iteratively.

My solution with recursion.

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

Class solution (object):
def isSymmetric (self, root):
if it is not root: return True #None is symmetric
returns self.isMirror (root.left, root.right)

def isMirror (self, l, r):
yes no l and no r: returns True #base case 1
if it is not or not r: returns False #base case 2
if l.val! = r.val: return False #base case 3
# case of recovery
left = self.isMirror (l.left, r.right)
right = self.isMirror (l.right, r.left)
go back to the left and right

I assumed it as a decent solution to this problem but I got a low score

Runtime: 32 ms, faster than 24.42% of Python's online shipments for Symmetric Tree.
Memory usage: 12.2 MB, less than 5.08% of Python's online presentations for Symmetric Tree.

How could I improve my solution?