English for German tree much shorter than German for English
The German for English tree has 125 levels, but it's reverse tree, English for German, has just 75. How come it has so much less content? Can't Duo just use the same material, but swap the questions for the answers?
Then it would be pointless to do the reverse tree, because it would be the same content. Also, I'm assuming the DE->EN tree has English names instead of German ones, and it would be pointless to teach certain words like 'Weihnachtsmarkt' in that tree because in most (if not all!) English-speaking countries there is no such thing.
German grammar is much more complicated than English grammar - they have three noun genders, for example, and formal and informal pronouns and verb conjugations. English also doesn't have adjective endings, or two-way prepositions. So it certainly makes sense, given the German grammar complexities, that the German tree for English speakers would be quite a bit longer than the reverse tree.