jQuery Grid Plugin - jqGrid

Hi,

Using two columns, i created a group header named as 'Group1'

{startColumnName: 'name', numberOfColumns: 2, titleText: 'Group1'},
Using next two columns created another group header named as' Group2'

{startColumnName: 'tax', numberOfColumns: 2, titleText: 'Group2'},

My code : http://jsfiddle.net/ZGDa2/18/

Can i create another header names as 'Groups' over subheaders Group1 and Group2 ??? What i have to define for this ???

This is very important for me because in my case headers can be of multilple n levels.

Please reply as soon as possible, it is very urgent.

Thanks

Naresh