What are the options after finishing a language course and receiving a Golden Owl?
BY reverse tree do you mean starting again, but from the bottom this time? And what is laddering languages?
Reverse tree would mean to do the tree in reverse languages - so if you finished the Portuguese for English speakers tree for example, you'd do the English for Portuguese tree instead. I'm doing it for Dutch and I've picked up on lots of new words. Laddering languages would be, for example, learning Portuguese from English, then taking the German course for Portuguese speakers and then the French course for German speakers and so on.
Maybe just my opinion, but if you can cope with most of the material on Duolingo, you should just start learning more from real world materials, whether that be songs, websites, books, tv, talk radio etc. Music is my particular poison, it's very helpful for locking down vocabulary.