input: 
  def is_subtree(T: Node, S: Node) -> bool:
      """ Check if the binary tree S is a subtree of binary tree T.
      >>> from node import Node
      >>> T = Node(26)
      >>> T.right = Node(3)
      >>> T.right.right = Node(3)
      >>> T.left = Node(10)
      >>> T.left.left = Node(4)
      >>> T.left.left.right = Node(30)
      >>> T.left.right = Node(6)
      >>> S = Node(10)
      >>> S.right = Node(6)
      >>> S.left = Node(4)
      >>> S.left.right = Node(30)
      >>> is_subtree(T, S)
      True
      >>> T = Node(26)
      >>> T.right = Node(3)
      >>> T.left = Node(10)
      >>> S = Node(26)
      >>> S.right = Node(3)
      >>> is_subtree(T, S)
      True
      """
  
output:     if T is None or S is None:
          return False
      
      def is_identical(node1, node2):
          if node1 is None and node2 is None:
              return True
          if node1 is None or node2 is None:
              return False
          return (node1.val == node2.val and
                  is_identical(node1.left, node2.left) and
                  is_identical(node1.right, node2.right))
      
      def find_subtree(T, S):
          if T is None:
              return False
          if is_identical(T, S):
              return True
          return find_subtree(T.left, S) or find_subtree(T.right, S)
      
      return find_subtree(T, S)