tree.py

class Node(object):

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

def max_of_tree(root):
    if not root:
        return 0

    max_left_path = max_of_tree(root.left)
    max_right_path = max_of_tree(root.right)
    return max(max_left_path, max_right_path) + root.val

node_20 = Node(54)
node_21 = Node(55)
node_23 = Node(3)

node_10 = Node(1, node_20, node_21)
node_11 = Node(2, None, node_23)

root = Node(1, node_10, node_11)

print max_of_tree(root)