Please tell me this is compatible with Johnny decimals https://johnnydecimal.com/
Why have I never heard of this before? And I'd really like to see some example top-level hierarchies. And I'd ask, still, is is unnecessarily hierarchical? If you only have 10 categories below "20 Finance", why not just stick the (maximum) 10 categories under 20-29 in the top level? You'd still have the conceptual grouping under 2x, but without the indirection.
I would also like to see more examples. I'm an academic, if anyone here is also one and has implemented this system I'd be very interested in seeing what your tree looks like!