How to Calculate the Height of a Binary Tree

class Node(object):

    def __init__(self, value):
        self.value = value
        self.left = None
        self.right = None


class BinaryTree(object):

    def __init__(self, root):

        self.root = Node(root)

    def height(self, node):

        if node is None:

            return -1

        left_height = self.height(node.left)

        right_height = self.height(node.right)

        return 1 + max(left_height, right_height)

tree = BinaryTree(1)
tree.root.left = Node(2)
tree.root.right = Node(3)
tree.root.left.left = Node(4)
tree.root.left.right = Node(5)

print(tree.height(tree.root))