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How to create a collapsible sidebar with tree structure of uploaded files

I am newbie and looking for a collapsible sidebar with the list of uploaded files.
I am able to get a basic one but navigation is not good and also it is not collapsible. I see some bootstrap ones(e.g https://bootsnipp.com/snippets/DV41) but not sure how to use them?

Do I download them and store for the app to access? Any details on how-to is appreciated. The documentation says download and store the css and js files, but how about HTML to display the equivalent UI(here it is sidebar). Should I put the corresponding HTML into my layout? But the syntax is different from the DASH syntax(e.g it has div class).