I don't like to think of it as compile-time trees. It basically only allows you to construct complicated structures but doesn't allow you to examine them at compile time (that would require constexpr functions in C++; can't be done in C). It's honestly not a very impressive feature.

Look at clk driver code for sunxi in mainline kernel. That uses it a lot.

https://elixir.bootlin.com/linux/latest/source/drivers/clk/s...

Maybe for making a declarative GUI system in C? I’ve never seen this before, so I’m not sure it could be done.

A hardcoded trie for string matching, perhaps?

I used it to describe neural network architectures.