multiple cascading dropdown filtering from using jquery json

How can i add multiple dropdown list and group them in a way that when i select any dropdown list it will display me the results accordingly from database(sql server).

I have duplicate values in database and i want to group them when selecting from dropdown list.

 

I am using one of the code from this website: 

 https://www.c-sharpcorner.com/article/mvc-show-record-using-cascading-drop-down-list-in-mvc-usin/

 

 

Please someone help me with  javascrip looping and controller linq query!!!