Adding the collapse/expand function to a subgroup

Good morning,

I'm quickly getting a handle on building some very nice reports with SSRS.

When I do the first grouping of data, the expand/collapse function is added to the top level. Works great. When I add a subgroup, the expand/collapse (+) function is not included. I'm not able to find a property setting that accomplishes this.

Thanks to whoever can point me in the right direction!