sub write_pie_chart {
    my $data_ref = shift;

    my $chart = $workbook->add_chart( type => 'Pie' );

    # Configure the chart.
    $chart->add_series(
        categories => '=Table!$B$7:$B$12',
        values     => '=Table!$C$7:$C$12',
    );
    $chart->set_title( name => 'chart name' );