You are able to choose Select List (cascading) as Statistic Type when configuring a gadget. However, the results will also be separated by the parent select list.

As can be seen from the screenshot, issues from parent 1 are displayed separately.

It would help if you can choose to display it based only parent select list (and not display the child list). Then it will be easier to see the difference between the parent select lists.

The screenshot is of pie chart, but it should be applied to all gadgets.