old_contents: class Leaf(object):
      '''Create leaf.'''
      def __init__(self, left=None, value=None, right=None):
          self.left = left
          self.value = value
          self.right = right
  
  
  class Tree(object):
      '''Create tree'''
      def __init__(self, root=None):
          self.root = root
  
      def search(self, value, leaf):
          if leaf is None or leaf.value == value:
              return leaf
          elif value < leaf.key:
              return search(value, leaf.left)
          else:
              return search(value, leaf.right)
  
      def insert(self, value):
  
          if node is None:
              self.root = Leaf(value=value)
          elif 
  
new_contents: class Leaf(object):
      '''Create leaf.'''
      def __init__(self, key, left=None, right=None):
          self.left = left
          self.key = key
          self.right = right
  
  
  class Tree(object):
      '''Create tree'''
      def __init__(self, root=None):
          self.root = root
  
      def search(self, key, leaf):
          if leaf is None or leaf.key == key:
              return leaf
          elif key < leaf.key:
              return self.search(key, leaf.left)
          else:
              return self.search(key, leaf.right)
  
      def contains(self, key):
          result = self.search(key, self.root)
          if result is None:
              return False
          else:
              return True
  
      def insert(self, key, leaf):
          if leaf is None:
              return Leaf(key)
          elif key == leaf.key:
              return Leaf()
          elif key < leaf.key:
              return Leaf(leaf.key, self.insert(key, leaf.left), leaf.right)
          else:
              return Leaf(leaf.key, leaf.left, self.insert(key, leaf.right))
  
subject: add insert and contains.