Tree Height Calculator

Given a binary tree, write a program to calculate its height. The height of a tree is the number of edges in the longest path from the root node to a leaf node. If a tree has no nodes, its height is -1. If it only has a root node, its height is 0. Input format: A series of integers in level order, where 'N' represents a null node. For example, the input `1 2 3 N N 4 5` represents the tree: 1 / \ 2 3 / \ 4 5 Output format: An integer representing the height of the tree. Example: Input: 1 2 3 N N 4 5 Output: 2