add a collapsible tree view into markdown

[ben-marengo-msmg]

i'd like to display a tree of items that sit naturally in a hierarchy

the functionality should be exactly like this - https://www.w3schools.com/howto/howto_js_treeview.asp

from that link, ive tried adding the given:
html to docs/my_markdown.md
js to docs/javascripts/extra.js
css to docs/stylesheets/extra.css

the html just renders as a static bulletpoint list. how can i get it to render like on the link's demo?