To add a Parent Group to a Tablix, please
- Select the Tablix and Right-click the Column Groups => Advanced.
- Go to the first Row Group, Click Add Group => Parent Group
- If you want to make the Parent Group expandable, make the current Group hidden first (Properties => Hidden = True) and Set ToggleItem = the Parent.
- Add a total between the two new groups, and set up the fields to calculate the group total if needed (looks better at least.)
If you wonder why I write this down => maybe this is rather a note for me, because I always tend to forget how to do this, and end up wasting a lot of time trying to find out the correct solution.