I'm aware of the solution described https://www.telerik.com/forums/is-there-a-way-to-set-a-treeview-busy-like-grid's-loading but it would be nice to have a way to control build-in loading indicator instead of implementing a custom one.
In a scenario when the data is stored in the state and fetch children immediately returns empty observable and then when data is available and emitted to the source observable you can't see the loading indicator.
An example:
https://stackblitz.com/edit/angular-wtvg2h?file=app/categories.service.ts
Click to expand a category, the "expand" icon is changed to "expanded" but no data is available yet. Two seconds later when data arrives it looks fine, but it would be really good to improve users experience and show a build-in loading indicator while data is not yet available
