input: from typing import Optional
  
  
  class TreeNode:
      def __init__(self, x):
          self.val = x
          self.left = None
          self.right = None
  
  
  def are_similar(root1: Optional[TreeNode], root2: Optional[TreeNode]) -> bool:
      """
      Check if two binary trees are similar. Two trees are similar if they have the same
      structure and the same values at corresponding nodes.
      
      >>> tree1 = TreeNode(1)
      >>> tree1.left = TreeNode(2)
      >>> tree1.right = TreeNode(3)
      >>> tree2 = TreeNode(1)
      >>> tree2.left = TreeNode(2)
      >>> tree2.right = TreeNode(3)
      >>> are_similar(tree1, tree2)
      True
      
      >>> tree3 = TreeNode(1)
      >>> tree3.left = TreeNode(4)
      >>> tree3.right = TreeNode(3)
      >>> are_similar(tree1, tree3)
      False
      """
      if root1 is None and root2 is None:
          return True
      if root1 is None or root2 is None:
          return False
      if root1.val != root2.val:
          return False
      return are_similar(root1.left, root2.left) and are_similar(root1.right, root2.right)
output:     if root1 is None and root2 is None:
          return True
      if root1 is None or root2 is None:
          return False
      if root1.val != root2.val:
          return False
      return are_similar(root1.left, root2.left) and are_similar(root1.right, root2.right)