Add Sub-Menu Page in Existing WP-Admin Plugin/Page

You can add custom page in existing plugins using below code snippet. Paste it into functions.php

function theme_options_panel(){
add_submenu_page('edit.php?post_type=product', 'Trip Activity Log', 'Trip Activity Log', 'manage_product_terms', 'trip-log', 'supra_trip_log');
}
add_action('admin_menu', 'theme_options_panel');

function supra_trip_log(){
/* Custom Code Will Display Here*/
}