Not being able to complete your native language's tree should be an achievement.
I always lose all my 3 lives towards the end when I try to take the test to pass the entire Romanian tree. I'm sad.
Romanian is a language with an extensive system of contractions for object pronouns and short forms of the verb 'a fi'. Sometimes these are not recognized, or some other silly thing happens. As an example, you can use the preposition 'de' to show quality or you can use an adjective, making 'orchestră de cameră' and 'orchestră camerală' just as correct, but duolingo doesn't consider the former correct.
Most I can do is report all these instances :)
The course was designed for the user to learn the formats presented prior to testing in each lesson. This was to be able to release the course as soon as possible as we've been the longest incubated course (at least during the time I was there). We are well aware of this issue and are looking forward to fixing these problems in the upcoming tree (but for that we need more contributors) :))