input: 
  def isSubTree(T, S):
      """
      Check if a binary tree S is a subtree of another binary tree T.
      
      >>> T = Node(1)
      >>> T.left = Node(2)
      >>> T.right = Node(3)
      >>> T.right.left = Node(4)
      >>> T.right.right = Node(5)
      
      >>> S = Node(3)
      >>> S.left = Node(4)
      >>> S.right = Node(5)
      
      >>> isSubTree(T, S)
      True
      
      >>> S = Node(3)
      >>> S.left = Node(4)
      >>> S.right = Node(6)
      
      >>> isSubTree(T, S)
      False
      """
  
      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))
output:     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))