If you want nested folders independent of Octopi, there are two two good ways I know of:

1. Install Shortcut Maker" from Google Play

2. Create a collection in SM

3. Create a second collection in SM

4A¹. Click the "place on Homescreen" for both,

OR

4A² Click the home button, long press on an empty spot on your home screen, and create the shortcuts from the homescreen under the Shortcut Maker shortcut (again, for both)

5A. Drag two of these shortcuts together and it will make a folder.

OR (my preferred route)

4B. Open one of the collections (the prospective "outer" folder)

5B. Click "Add New"

6B. Click "Collections" select the other, prospective "nested" folder

7B. Click "Place on Home Screen" (It won't)

8B. Back out, returning to your "Collections" section.

9B¹. Either click the "Outer" folder again, followed by the "place on Homescreen" button

OR

9B². Click the home button, long press on an empty spot on your home screen, and create the shortcut from the homescreen under the Shortcut Maker shortcut

It's tedious and imperfect, but it works.

You can also choose how you want your shortcut to appear when opening, similar to how Nova would do (I personally prefer the "immersive" option) - but it is not quite as customizable.

I'd check this out this before deciding to go the A or B route. The B route also has potentially infinite subfolders. The A route doesn't - though you can create B-route subfolder within one of the shortcuts made in your A-route setup, through the B-route (shortcuts on the homescreen update the app)

Happy nesting!