Any English native speakers here, question: I have read that you say "at the top" for things that can fluctuate, e.g. "at the highest level; at the top of the rankings. And that for things that are rather solid and where the top is clearly the top and always stays the top, you would have to say "on the top", e.g. On the top of the mountain/tree. Correct? Thanks
That makes sense. Also I think of something physical/solid, which is why the cat on the tree doesn't make sense to me. Most trees don't have tops big or stable enough for a cat to get on. You could put a star on top of a Christmas tree. A bird could perch on top of a tree. It's funny, you don't realize when you grow up speaking a language why certain things are the way they are. And English has a lot of local variation, as seen in previous comments. So keep in mind, yes, I'm a native speaker, but these are just my personal thoughts, and that will vary a lot from person to person. Many of us do not use fully proper English, especially when speaking!
The top of a tree is not solid. A cat wouldn't be able to be on top of a tree, because the branches would be too thin to carry it. To be on top it would be visible, standing on the tree free from foliage. The cat is in the top, because it isn't visible, but sits in the top part of the tree hidden in it.
I don't like the translation "juu ya" meaning "at the top of". "Juu" as a noun means "top;" however, "juu ya" as a preposition is translated: 1. over, 2. above, on 3. concerning, about. According to my dictionary, "juu kwa juu" is the proper translation "at the top." So, in my opinion, the proper translation of "Pana paka juu ya mti" should be, "There is a cat on the tree."