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.
I've been using Golang professionally for about a decade. In that time the only place I've ever needed to use a tree map was an interview that specifically called for it.
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.
