Is it possible to add sub-menu to the vaadin demo app ? ( https://github.com/vaadin/dashboard-demo )
Yes, but the menu that demo app uses don’t have any built in feature for hierarchy, so you’d need to built that by yourself. I guess it should be pretty easy to add, especially if you don’t care about smaller screensizes, which might need some separate design for good UX.
cheers,
matti