code: def is_symmetric_iterative(root):
      if root is None:
          return True
      stack = [[root.left, root.right]]
      while stack:
          left, right = stack.pop()  # popleft
          if left is None and right is None:
              continue
          if left is None or right is None:
              return False
          if left.val == right.val:
              stack.append([left.left, right.right])
              stack.append([left.right, right.left])
          else:
              return False
      return True
  
label_desc: Use image node_id 3 for calling a global function with example usage: is_symmetric_iterative(root) and returns: True, True, False, False