It's not about creating a tree map, it's just about using one. Maybe even one provided by a library, doesn't matter. I'm sure that 95% of the developers will need a tree map at least once in their career.
Whose usage are you trying to optimize the language for? Golang is not a good academic language. But it is extremely good for actually solving problems with code.
More compelling ones are sets, ordered maps, a generic sync.Map, optionals (nulls suck!), abstractions over channels - badly needed!
I wouldn't consider any of those to be academic.