What is the test case which is not covered in the code written by me



the above is a link to a solution of the BST problem. I am yet to start my second year and i am new to DS, using the concepts this is my first implementation. I can’t figure out why the CodeChef evaluator is giving ‘wrong answer’ every time. Is it any test case which i have forgotten to incorporate or some constrain condition which i am missing out? thank you.