Hi Billy,
Thank you for contacting Syncfusion Support.
We have prepared a sample for your requirement. In this sample, We have applied VisualStyle as Blend and set the ItemHeight of the GroupViewItem as 0 to achieve your requirement and it can be downloaded from the below link.
Output
You can refer the below link for more details about GroupBar.
Please check the above solution and let us know if it is helpful.
Regards,
Venkateshwaran V.R.