Here’s an idea I’ve never tried but have had in my mind for a while.
Countries already have a numerical identifier that everyone agrees on: their international dialling code. Australia is 61, for example. The UK 44. USA is 1 obviously, is Canada the same? That’s unhelpful but hey.
So do many cities and states. I know the USA’s area codes are well defined. Australian states each have a code.
Could you construct numbers for the first part of your tree, up to the point where you reach your projects/clients, using these already-known numbers?…
Otherwise I think I’d just be advocating for a use-the-alphabet-with-numbers-after-the-items approach like explained here.