Help me in solving BTPOSTORDER problem

help
,
1

My issue

Please give me solution code for it

My code

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

def post_order_traversal(root):
    # complete this

Learning course: Data structures & Algorithms lab
Problem Link: PostOrder Traversal in Data structures & Algorithms lab