I've finished my German Tree!
Esperanto for Spanish Speakers, English for Spanish, Spanish for English, German for English and Esperanto for English.
Cool. So far I've only completed Spanish for English, but I'm pretty close to finishing my French Tree as well.
It's easy cause it mixes elements from different language roots, and it's like my native language Spanish. There are not many gramatical rules for learning it, so it was easy for me to remember the vocabulary, verbs, pronunciation,etc. It has also helped me to remember other languages I'm doing, like Russian, Italian or Portuguese.