Improved group collapse/expand controls
When groups (e.g. level 1) and sub-groups (e.g. Level 2) share the same last row, the collapse/expand control (+/-) for level 2 sub-group is omitted and the level 1 control is overloaded to expand the last sub-group. Suggest you explicitly provide expand/collapse controls for groups and sub-groups even if they end up on the same row.