input: Write a function to check if a given binary tree is a subtree of another binary tree. If it is a subtree, return True; otherwise, return False. If both trees are empty, return True.
  def isSubTree(T, S):
      if S is None: 
          return True
      if T is None: 
          return False
      if areIdentical(T, S): 
          return True
      return isSubTree(T.left, S) or isSubTree(T.right, S)
  
  def areIdentical(T, S): 
      if T is None and S is None: 
          return True
      if T is None or S is None: 
          return False
      return (T.data == S.data and areIdentical(T.left, S.left) and
          areIdentical(T.right, S.right))
  
  # Test cases
  assert isSubTree(None, None)==True
  assert isSubTree(Node(1), None)==True
  assert isSubTree(None, Node(1))==False
  assert isSubTree(Node(1, Node(2), Node(3)), Node(2))==True
  assert isSubTree(Node(1, Node(2), Node(3)), Node(1))==True
  assert isSubTree(Node(1, Node(2), Node(3)), Node(1, Node(2), Node(4)))==False
  assert isSubTree(Node(1, Node(2, Node(4), Node(5)), Node(3)), Node(2, Node(4), Node(5)))==True
output: def isSubTree(T, S):
      if S is None: 
          return True
      if T is None: 
          return False
      if areIdentical(T, S): 
          return True
      return isSubTree(T.left, S) or isSubTree(T.right, S)
  
  def areIdentical(T, S): 
      if T is None and S is None: 
          return True
      if T is None or S is None: 
          return False
      return (T.data == S.data and areIdentical(T.left, S.left) and
          areIdentical(T.right, S.right))