input: def isSubTree(T, S): 
      """Check if the given binary tree S is a subtree of binary tree T.
      >>> T = Node(26)
      >>> T.left = Node(10)
      >>> T.left.left = Node(4)
      >>> T.left.right = Node(6)
      >>> T.left.left.right = Node(30)
      >>> T.right = Node(3)
      >>> T.right.right = Node(3)
      >>> S = Node(10)
      >>> S.left = Node(4)
      >>> S.left.right = Node(30)
      >>> S.right = Node(6)
      >>> isSubTree(T, S)
      True
      >>> S = Node(10)
      >>> S.left = Node(7)
      >>> S.right = Node(6)
      >>> isSubTree(T, S)
      False
      """
output:     if not T and not S:
          return True
      if not T or not S:
          return False
      if T.val == S.val:
          return (isSubTree(T.left, S.left) and isSubTree(T.right, S.right)) or isSubTree(T.left, S) or isSubTree(T.right, S)
      return isSubTree(T.left, S) or isSubTree(T.right, S)