input: Write a python function to insert and find nodes in a binary search tree.
  assert root.insert(10) is None
  assert root.insert(5) is None
  assert root.insert(15) is None
  assert root.find(10) == 'Found'
  assert root.find(5) == 'Found'
  assert root.find(15) == 'Found'
  assert root.find(7) == 'Not Found'
output: class TreeNode:
      def __init__(self, key):
          self.left = None
          self.right = None
          self.value = key
  
      def insert(self, key):
          if self.value is None:
              self.value = key
          else:
              if key < self.value:
                  if self.left is None:
                      self.left = TreeNode(key)
                  else:
                      self.left.insert(key)
              else:
                  if self.right is None:
                      self.right = TreeNode(key)
                  else:
                      self.right.insert(key)
  
      def find(self, key):
          if self.value is None:
              return 'Not Found'
          if self.value == key:
              return 'Found'
          elif key < self.value:
              if self.left is None:
                  return 'Not Found'
              return self.left.find(key)
          else:
              if self.right is None:
                  return 'Not Found'
              return self.right.find(key)
  
  root = TreeNode(10)