TreeGrid group summary

Can you provide code example of displaying group summary for different columns of a treegrid using Smart GWT. I'm using SmartGWT version 3.1. I could not get the group summary to show up in TreeGrid. ListGrid is working fine.

Here's my java code snippet -
Creating TreeGrid and setting ShowGridSummary and ShowGroupSummary to true.
TreeGrid treeGrid = new TreeGrid();
treeGrid .setShowGroupSummaryInHeader(true);
treeGrid .setShowGridSummary(true);
treeGrid .setShowGroupSummary(true);

....
Setting ShowGridSummary and ShowGroupSummary to true for some of the TreeGridFi
TreeGridField treeField = new TreeGridField("test", "test");
treeField.setSummaryFunction(SummaryFunctionType.S UM);
treeField.setShowGridSummary(true);
treeField.setShowGroupSummary(true);

Thanks.