python BinarySearchTree easy question

__init__(self)

Initializes a tree node to be empty. Attribute values are set to None..

add(self, val)

Adds a node with the value val to the tree so as to maintain the binary search tree property (see above).

find(self, val)

Returns: a reference to the tree node with value val if it exists, None otherwise.

__str__(self)

Returns a string representation of the tree. For the purposes of this assignment, this is defined as follows. Given a tree T:

If T is None (i.e., empty), return the string "None" (the quotation marks simply indicate that the value is a string; they are not part of the string itself).

Otherwise, suppose that T has a root node with value val and left and right subtrees T_left and T_right. Return the string

"({:d} {} {})".format( val, str(T_left), str(T_right))