Get name of file that is including a PHP script

Here is an example of what I am trying to do:

index.php

<ul><?php include("list.php") ?></ul>

list.php

<?php
    if (PAGE_NAME is index.php) {
        //Do something
    }
    else {
        //Do something
    }
?>

How can I get the name of the file that is including the list.php script (PAGE_NAME)? I have tried basename(__FILE__), but that gives me list.php.