Percent of tree completed
I'd like to be able to see what percentage of lessons have been completed on my tree. I think it would be a better gauge of how far I am than levels and coins which are affected by skill practices.
But what if the tree grows? I'm hoping more and more lessons will be added so that the whole language is covered, including things like the words I'm going to need for my studies in biology, and more diverging branches will be added.