input: def isSubTree(T: Node, S: Node) -> bool:
      """ This function checks if a binary tree S is a subtree of a binary tree T.
      >>> 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)
      >>> isSubTree(T, S)
      True
      >>> S = Node(10)
      >>> S.right = Node(6)
      >>> S.left = Node(4)
      >>> S.left.right = Node(25)
      >>> isSubTree(T, S)
      False
      """
output:     if T is None and S is None:
          return True
      if T is None or S is None:
          return False
      if T.value == S.value:
          return isSubTree(T.left, S.left) and isSubTree(T.right, S.right)
      return isSubTree(T.left, S) or isSubTree(T.right, S)