The header row (the group headers in a GridView, or a parent row in a TreeListView) stays in the screen while scrolling until all the children rows have been scrolled.

The feature is available in R3 2017 Release of UI for WPF.
Check what's new in R3 2017 here: 
http://www.telerik.com/support/whats-new/wpf/release-history/ui-for-wpf-r3-2017