How to change Group Header Font in Crystal report Left Most Group Tree?

Hi Dears!
I am using crystal report 10 with C# 2005. I have an issue that i want to change the font of Group Header Text that is visible when we click on Toggle Group Tree button and a tree pane is visible towards the left side of report viewer.
I have goggled a lot but unable to find any hint. Any idea or help would be highly appreciated .
Thanks in advance.

The group tree area is part of the report viewer. As far as I know the only properties of the viewer available at design time or run time have to do with the behavior of tool bars and such, not fonts. I would like to be able to accomplish the same thing, so I look forward to answers.