Implementation of trees in Python

gistfile1.py

class Node:
    def __init__(self, left, right):
        self.left = left
        self.right = right

def n(left=None, right=None):
  """Shortcut method for making a tree."""
    return Node(left, right)

test = Node(n(), n())   

def height(node):
    if node is None:
        return -1
    elif node.left is None and node.right is None:
        return 0
    else:
        return max(height(node.left), height(node.right)) + 1

def isAVLTree(node):
    if node is None:
        return True
    elif node.left is None and node.right is None:
        return True
    elif (isAVLTree(node.left) and isAVLTree(node.right)) and \
    abs(height(node.left) - height(node.right)) <= 1:
        return True
    else:
        return False