You have now conquered your shiny Dutch 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 Dutch lessons recently but you still have to finish 145 more sessions to get all of your skills to the Legendary Level — check back here when you practice a few more lessons to see how soon you're supposed to level-up your Dutch tree. The longer you practice, the more accurate is the prediction.
Keep going! =)