With these files, you can select multiple cascade selection fields by filtering each selection.
This project is applicable to the Wordpress CMS, contains 3 separate files:
-functions.php -main.js -form.php
I have divided every single action for the right placement in the file, insert the code directly into your functions and into your main.js and create a .PHP file with any name for the HTML selection fields. Obviously you will have to change the name of your TAXONOMY
Remember to add javascript for your main.js and possibly bootstrap 3 or 4 if you are going to stylize the selection form