input: Write a function to determine if a binary tree \( S \) is a subtree of a binary tree \( T \).
  
  class Node: 
      def __init__(self, data): 
          self.data = data 
          self.left = None
          self.right = None
  
  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(Node(1), Node(2)) == False
  assert isSubTree(Node(1), Node(1)) == True
  assert isSubTree(Node(1), None) == True
  assert isSubTree(None, Node(1)) == False
  
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))