Suggestion for what could/should come next:
I think that once the tree (and perhaps the reverse tree) have been completed, there should be a new level, purely in the target language, giving e.g. impulses to be made into sentences/questions, and questions to be answered. - in all languages.
Yes, thank you. I have already tried the Spanish ones. They are a nice extension, especially as they are almost completely in the target language. I haven't finished them, yet, and hope that they will develop past the spoon feeding style of the first ones.