Show all categories and all subcategories

Hi - first post here, I hope I'm writing to the right place.

I've just been thrown into an Opencart project, and after a bit of time googling, want to ask you guys if there's a pre-canned solution, or if it's something that needs to be written from scratch...

Essentially, what I have is a store with 8 master categories.

Each of those master categories, has 4-8 children, and each of those children also has 4-8 children.

What I'm wanting to do is, if you click any of the master categories, to show each of that categories children, as well as each of those children's children.

For instance (i want this to all display on a single page):

(master) - COMPUTERS

(child) - MAC

(sub children) - MacBooks - Macbook Pro's - Macbook Airs - etc.

(child) - PC

(sub children) - Dell - HP - Lenovo - Acer


I found a Subcategory extension that shows images of subcategories (in refine search), but that only gives me the master category, and the subcategories of that category, but non of that subs children (not enough recursion).

Anyways. If this makes sense, is there an extension out there that already does this sort of thing? Or is this something that would need to be built from scratch? Any pointers on the first would be appreciated! And if its the second, at least that's good info to bring to the boss to determine if he wants to budget for that.

Many thanks!

(I've got other things to work on, so I'm going to leave the categories and children alone for the next couple days in hopes anyone has a suggestion)