You have now conquered your shiny German golden owl. Yay!Now it's time to advance to the next tree level and probably discover more content and harder lessons with each level.
You didn't do enough German lessons recently but you still have to finish 160 more sessions to get all of your skills to Level 4 — check back here when you practice a few more lessons to see how soon you're supposed to level-up your German tree. The longer you practice, the more accurate is the prediction.
Keep going! =)