old_contents: class BSTNode:
      def __init__(self, data, left=None, right=None):
          self.data = data
          self.left = left
          self.right = right
  
  class BST:
      def __init__(self, data=None):
          if not data:
              self.root = None
          else:
              self.root = BSTNode(data)
  
new_contents: class BSTNode:
      def __init__(self, data, left=None, right=None):
          self.data = data
          self.left = left
          self.right = right
  
  class BST:
      def __init__(self, data=None):
          if not data:
              self.root = None
          else:
              self.root = BSTNode(data)
  
      def insert(self, data):
          new_node = BSTNode(data)
          if self.root is None:
              self.root = new_node
          else:
              temp = self.root
              while temp is not None:
                  if data <= temp.data:
                      if temp.left is None:
                          temp.left = new_node
                          break
                      else:
                          temp = temp.left
                  else:
                      if temp.right is None:
                          temp.right = new_node
                          break
                      else:
                          temp = temp.right
  
subject: insert iterative for bst