How to display subcategories in a nested menu on the left panel

Hello, I am looking for help on the sidebar on the category page. Is there a way to display the subcategories (with a +) so user can easily check the subcategories / category that they would like to filter for? It is currently only showing the main categories and the user has to select a specific category in order to be brought to a page that has a drop down for that subcategory. 

Basically aspiring to create something like the screenshot on the right below.

Thank you!

Hi,

What is site url? We can take a look