Hi, I have exactly the same need for the osticket v1.14
And I've founded a lot similar subjects/topics of poeple having the same need on this forum.
I think it is one of the biggest lack of OsTicket atm. OsTicket's engine has got all prerequires to make it work (at list the basic structure of "help topic" / "sub help topic" hierarchy), but the javascript code which would split that "sub / help topics" is missing from the user form.
A few years ago, on this forum, a member named @sosamv coded and shared a "mod" for v1.9 which was regrouping help-topics / sub-topics into a tree list. Like that :

Here is the original post link, and a preview hereunder :
Hello everyone. Here's the mod as promised. This mod was tested with the latest version of osTicket-v1.9.5.1 and it might not work with older versions. Just overwrite the files in the appropiate folders and should work right away. If you would like to see what was actually changed, do a ctrl+f for "@CHANGED".Dynamic forms are working, "Public" and "Disabled" options for the help topics too.Hope you guys like it,sosamv
osticketHTTree.zip
I hope someone else could develop and share such a plugin or mod.
It would be great to have it included in the next version of OsTicket.
Any fresh news about that @ntozier ? 🙂