¡Yo terminé el arbol inverso!
I never thought I would be able to finish one tree, let alone two! I highly recommend it, as I feel my Spanish skills have greatly improved! I learned much more vocabulary and really cemented the "old" words into my head by doing so much repetition. It seemed to me that the grammar was more complicated, probably because it was designed for native Spanish speakers, which was fantastic practice.
I suppose my next Duolingo goal will be to reach Level 25 in both trees, but for now I'm just going to bask in this great feeling of accomplishment!