I would like to be able to nest bookmarks by creating, for example, a nest of bookmarks in one file and then in another file (which is still part of the book) using the same name assigned to the bookmark nested in the previous file, so that I can continue to insert content within the same nest.
The result would be = 1 large group containing all the bookmarks I am interested in.

This could be done by taking a cue from the variant/variable renaming system that currently exists in Figma.

For example, if I want to put the bookmark ‘Spruce’ in the ‘Trees’ folder (which is, however, in a different file within the InDesign book), but at the moment I am in a different file, if I write in the rename space: Trees/Fir, InDesign creates a group between the two and when I export the pdf file I already find the bookmarks ready to be clicked on.