Is French the longest tree?
It seems like French is the longest tree. All of my other ones are shorter.
I think the Italian tree is actually longer if we're talking about the number of lessons. I started both tress at about the same time and I've only done one brand new lesson per day in each language. At that pace it has taken about a year to get through the courses. I already finished the French tree about a month ago. I only have two lessons left in my Italian tree and will be done by tomorrow.
So, I think the Italian tree is longer than the French tree right now. I don't know if any other language trees are longer.
I'm guessing you're talking about the number of skills taught rather than words or lessons?
English: (Unsure) - What language are you learning from by the way?
So you were right. Out of the ones you're doing French is the longest. And while Esperanto was the shortest tree created so far, that record has now been broken by Japanese with 40 skills.
Found it out using this: https://www.duolingo.com/comment/12532694/What-are-the-longest-and-shortest-trees-on-Duolingo
Hope that was useful.