Expand Event for Grouping
 

I have written an Excel plug-in which retrieves data from a custom data
provider. I would like to implement a drilldown functionality. One of the
options would be to use the Group functionality and trap the 'Expand' or "+"
click to then dynamically retrieve the data. Is there and event that I can
trap?

I am using VS 2008, .Net 2.0 and C#.