Indeed going through the notebook tree, this will work as there are relatively limited amount of notebooks within this sub-stack. If we would apply this trough the use of labels it will be significantly harder to do the same in an organised matter. Since one note can contain a lot of labels, for me this could be to first date general info as #University #semester 1 # year one # course name # block 2 #lecture 4 and then note specific ones as #international law #conflict #humanitarian law # China. Finding a specific note by "going through the tag tree" requires me to find the right tags which can be complicated if multiple notes can contain similar labels and will overall take more time.
Furthermore, I think this approach is counter intuitive, as I think generally humans organise information in a more visual matter. Therefore, the ability to organise information this way, by introducing sub-stacks, will make retrieving some information faster and reduce the amount of Notebooks in a singe stack, improving the overall organisation and clean appeal. The absence of the feature I am advocating for is one of my earliest frustrations with Evernote and hope this function will be introduced. Now, all my previous semesters/years are placed in one stack with notebooks that are layered by year, course, type of note (lecture, skills lab, readings and assignment) in a disorganised matter, one extra stack layer could mitigate this problem.