If you need a three level menu, a select dropdown jump menu in your WordPress website, here is the solution.
Use this WordPress menu anywhere in post, page and widget using shortcode with your menu name like this > [ pim_dropdown_menu menu=’Main’ ].

Here is the gist of this multi level WordPress select menu, add this in your functions.php or code snippet plugin:
Hope that helps.
Author: Ali Qureshi
I am a web & mobile app developer based in Lahore. I have been developing creative, interactive, usable & successful web apps, web portals, php and Flash action scripting, REST apis, WordPress plugins & themes. In recent years, I have worked on Ionic, Angular and TypeScript for hybrid mobile apps, Flutter & Dart, React & React Native, and Swift native iOS mobile app development.