To keep the notes page under the 'Product' menu organized, it would be nice to be able to have folders to be able to rearrange notes into a specific folder. So when creating multiple notes for one notebook, the folder would contain all of the notes that make up each notebook.
Thank you for your idea. Great news -- this already exists. You can rearrange notes into a parent/child hierarchy by clicking the Rearrange button and then dragging one note into another. For this use case, you could create one note representing your notebook, then drag the related notes into that one to create the sub-notes. This article explains it in more detail.