"Do this tree again!"
Translation:Tee tämä puu uudelleen!
I'm guessing it's about how these Duolingo courses are referred to as trees. Not a very good sentence to teach in my opinion, since it doesn't make sense to people who are here "only" to learn a language and don't really follow discussions. And even those who do won't ever need this sentence outside of this app.
That row of circles on Duo's website and app is called the tree. This is a reminder that you can go back and do your favourite lessons again. You can do them all until you turn them all yellow, and if you want, you can do them again. Each time you will earn more points and learn more about your chosen language or languages.