distance BT python

# http://code2begin.blogspot.compile
# Program to find distance between 2 nodes in a given binary tree
# node class
class node:
    def __init__(self, element):
        self.data = element
        self.left = None
        self.right = None


# function to find and return the level of a node in binary tree
def level_of_node(root, data, level=-1):
    # if the tree is empty or if we reach a leaf node then return 0
    if root is None:
        return -1
    if root.data == data:
        return level + 1

    # check in the left subtree for the element
    # if found then return the level
    level_node = level_of_node(root.left, data, level + 1)
    if level_node != -1:
        return level_node

    # searching for the node in right subtree
    level_node = level_of_node(root.right, data, level + 1)
    return level_node


def least_common_ancestor(root, n1, n2):
    if root is None:
        return root

    if root.data == n1 or root.data == n2:
        return root

    left = least_common_ancestor(root.left, n1, n2)
    right = least_common_ancestor(root.right, n1, n2)

    if left is not None and right is not None:
        return root

    if left is not None:
        return least_common_ancestor(root.left, n1, n2)

    return least_common_ancestor(root.right, n1, n2)


# function that returns the distance between 2 given nodes
def distance_between(root, a, b):
    LCA = least_common_ancestor(root, a, b)
    return level_of_node(LCA, a) + level_of_node(LCA, b)



head = node(1)
head.left = node(2)
head.right = node(3)
head.left.left = node(4)
head.left.right = node(5)
head.right.right = node(6)
head.left.left.right = node(7)
head.right.right.left = node(8)
head.left.left.right.left = node(9)
head.left.left.right.left.left = node(10)
head.right.right.left.right = node(11)
print("Distance between nodes 6 and 10 is : " + str(distance_between(head, 6, 10)))
print("Distance between nodes 1 and 10 is : " + str(distance_between(head, 1, 10)))
print("Distance between nodes 11 and 10 is : " + str(distance_between(head, 11, 10)))