How long does it take to learn German
If I did 40 minutes a day, how would it take for me to the the whole "tree"?
It all depends on how comfortable you want to be before moving on; 40 minutes a day is plenty to make pace, but review is always good as well. Completing a tree can be done in a few weeks, but it really should take months to properly memorize the content. Learning a language is a long process and shouldn't be rushed too much! Good luck with your learning, hope you enjoy German enough to keep at it.