How to make a hierarchical / nested navigation rail?

[clstaudt]

I would like to arrange the items in a navigation rail into labelled groups, either by grouping them under a headline or merging them into a collapsible item. How could this be implemented with flet?

[FeodorFitsner]

Looks like you've already found a prototype: https://github.com/flet-dev/gallery

[clstaudt]

Great to have Collapsible items now. Is it also possible to group items in a navigation rail using headlines, like in the screenshot above?