1

Allow to group (in tree structure) of Activities.

Each node and leaf could be Activity itself (or virtual activity - void). Void activity is not selectable.

Why this feature?

I could imagine I created learning/study activity and attach Math, English, Biology, etc. activity to it.

When I came to university/school, I restart each subactivity with study activity.

I can also create activity for work (examples of subactivites):
Order
Magazine
Send

And, when client send me order, I place it on order activity (for example notes plasmoid). In next day, I will look at Magazine activity and if product is in magazine, I complete products from order, send it and cut order from order activity and paste to send activity.