Get all subcategories for a virtual category

[OvalMedia]

I have created a ViewModel that recusively renders all categories in a sidebar. Nothing fancy, just a static list of categories.
Now I would like to incorporate virtual categories into this. I see that your module renders all virtual subcategories inside the category filter, which I don't use. Magento's filter concept is complex enough, it is hard to keep track when filters and categories are mixed, so I tend to keep them separate.

My question: is there a way to get and render all (virtual) subcategories of a virtual category somehow?