I do something vaguely similar using
calibre:// URL links in a custom long text column.
Books are cross-linked with a
show-book, a
book-details, and one or more
view-book links. So it creates a network structure rather than a hierarchical structure which is what your 'grouping' scheme seems to imply.
I have pro-forma HTML snippets that I paste into a #links/Links long text custom column, e.g. :
Code:
<a href="calibre://show-book/_hex_-426f6f6b73/NNNN"><span style="color: #ffff00">Jump to release</span></a> ::: <a href="calibre://book-details/_hex_-426f6f6b73/NNNN"><span style="color: #ff55ff">Release details</span></a> ::: <a href="calibre://view-book/_hex_-426f6f6b73/NNNN/FORMAT"><span style="color: #00ff00">View FORMAT</span></a></p></div>
The "NNNN" gets replaced with the Book number (id), etc.
BR