What's the outcome?
Once you complete all the "tree" for a language, which level are you supposed to have? If you completed it for some language, can you share your thoughts? What are you able to do now, and what do you need more practice with?
You can complete the tree and still have almost no ability to carry on a conversation in the new language. In Spanish, one can complete the tree and have huge gaps in the language, having barely touched on many things, with very little explanation of grammar and syntax. You need more practice with everything, especially listening and speaking. I would liken it to taking a crash course in language in grad school, learning enough to pass a reading exam -- but one is not going to tune in to the local Spanish radio broadcast and follow with understanding. DL has value, but also has limitations. Thankfully, there are other free sites than can be used to shore up DL's weaknesses.