Graff's original suggestion works great...sorry, head slap, just too rusty here to see it and thought it had to be more complicated. The following code populates the combobox

sub PopulateComboBox {
    
    my $hash = shift;
    
    foreach my $key(keys (%$hash)){
        $MainWindow->FilterList->Add($key);
        foreach (@{$$hash{$key}}) {
            $MainWindow->FilterList->Add($_);
        }
    }
    $MainWindow->FilterList->SetCurSel(0);
}
[download]

many thanks