Thanks for the feedback! I was also embarrassed that there are so many ideas that combine Spaced Repetition with a note-taking tool.

But nonetheless, I still think LearnObit is the most special and the best of them. In any case, to explain your question, in the tree structure used by this app, a leaf is a card (so it's not about memorizing a nested list). Like this: Fruit> Apples> Taste: Sweet

And in the process of making the user memorizing, this app shows cards in clusters according to their position in the tree and the predicted rating and that's the point.