input: 
  def isSubTree(T, S):
      """
      Check if a given binary tree S is a subtree of another binary tree T.
      >>> root1 = Node(26)
      >>> root1.right = Node(3)
      >>> root1.right.right = Node(3)
      >>> root1.left = Node(10)
      >>> root1.left.left = Node(4)
      >>> root1.left.left.right = Node(30)
      >>> root1.left.right = Node(6)
      >>> root2 = Node(10)
      >>> root2.right = Node(6)
      >>> root2.left = Node(4)
      >>> root2.left.right = Node(30)
      >>> isSubTree(root1, root2)
      True
      >>> root3 = Node(1)
      >>> root3.left = Node(2)
      >>> root3.right = Node(3)
      >>> isSubTree(root1, root3)
      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))