class Solution:
    def helper(self, node1, node2):
      if node1 is None and node2 is not None:
        return False
      elif node2 is None and node1 is not None:
        return False
      elif node1 is None and node2 is None:
        return True
      if node1.val != node2.val:
        return False
      return self.helper(node1.left, node2.left) and self.helper(node1.right ,node2.right)
      
    def isSameTree(self, p: TreeNode, q: TreeNode) -> bool:
      return self.helper(p,q)