Create [my_pmpro_levels] shortcode which will work in sidebar widgets, etc.

my_pmpro_levels.php

<?php

/* Create [my_pmpro_levels] shortcode which will work in sidebar widgets, etc. */

function my_pmpro_levels($atts = NULL)
{
    ob_start();

    include(PMPRO_DIR . "/preheaders/levels.php");

    if(file_exists(get_stylesheet_directory() . "/paid-memberships-pro/pages/levels.php"))
        include(get_stylesheet_directory() . "/paid-memberships-pro/pages/levels.php");
    else
        include(PMPRO_DIR . "/pages/levels.php");

    $temp_content = ob_get_contents();
    ob_end_clean();

    return apply_filters("pmpro_pages_shortcode_levels", $temp_content);
}
add_shortcode('my_pmpro_levels', 'my_pmpro_levels');