What is after the tree ?
I have recently finished the Turkish tree, I felt so happy for this little achievement ,but now I really feel that I need extra support in learning Turkish from this specific app , I have tried to learn from other sources but I found that this is the best app ever, I enjoyed a lot using it indeed so if you can upgrade more extra materials or features so we can keep on learning from it, this would be great
If you have used the Duo app exclusively it should be worth logging on to the website to strengthen the tree. As a rule, on the website you get more typing exercises which is more difficult. Also, you must have missed the Tips and notes section under the lessons. The reverse tree of course is a good bet on Duo, as you will have to do most of the typing in Turkish.
I would look for a reverse course, that is English via Turkish. Maybe on Memrise?