implement the method below using Python:

class BinarySearchTree: 

def __init__(self, root: Optional[object]) -> None:  if root is None: self._root = None  self._left = None  self._right = None  else: self._root = root self._left = BinarySearchTree(None) self._right = BinarySearchTree(None) 

def num_less_than(self, item: object) -> int: """Return the number of items in this binary search tree that are less than . """ 

def items_at_depth(self, d: int) -> list: """Return a sorted list of all items in this BST at depth . Precondition: d >= 1. Reminder: you should not have to use the built-in 'sort' method or do any sorting yourself. """ 

 def levels(self) -> List[Tuple[int, list]]: """Return a list of items in the tree, separated by level. You may wish to use 'items_at_depth' as a helper method, but this also makes your code less efficient. Try doing this method twice, once with 'items_at_depth', and once without it! """