How can I add gap between bars using phpspreadsheet

Say, I have two set of data (x,y). I want to add gap between two bars in data series. Here is my code taken from phpspreadsheet sample.

$worksheet = $spreadsheet->getActiveSheet();
$worksheet->fromArray(
    [
        ['', 2010, 2011,],
        ['Q1', 12, 15, ],
        ['Q2', 56, 73, ],
        ['Q3', 52, 61, ],
        ['Q4', 30, 32, ],
    ]
);

$dataSeriesLabels = [
    new DataSeriesValues(DataSeriesValues::DATASERIES_TYPE_STRING, 'Worksheet!$B$1', null, 1), // 2010
    new DataSeriesValues(DataSeriesValues::DATASERIES_TYPE_STRING, 'Worksheet!$C$1', null, 1), // 2011

$xAxisTickValues = [
    new DataSeriesValues(DataSeriesValues::DATASERIES_TYPE_STRING, 'Worksheet!$A$2:$A$5', null, 4), // Q1 to Q4
];

$dataSeriesValues = [
    new DataSeriesValues(DataSeriesValues::DATASERIES_TYPE_NUMBER, 'Worksheet!$B$2:$B$5', null, 4),
    new DataSeriesValues(DataSeriesValues::DATASERIES_TYPE_NUMBER, 'Worksheet!$C$2:$C$5', null, 4),
];

// Build the dataseries
$series = new DataSeries(
    DataSeries::TYPE_BARCHART, // plotType
    DataSeries::GROUPING_STANDARD, // plotGrouping
    range(0, count($dataSeriesValues) - 1), // plotOrder
    $dataSeriesLabels, // plotLabel
    $xAxisTickValues, // plotCategory
    $dataSeriesValues        // plotValues
);

$series->setPlotDirection(DataSeries::DIRECTION_COL);

// Set the series in the plot area
$plotArea = new PlotArea(null, [$series]);
// Set the chart legend
$legend = new Legend(Legend::POSITION_RIGHT, null, false);

$title = new Title('Test Column Chart');
$yAxisLabel = new Title('Value ($k)');

// Create the chart
$chart = new Chart(
    'chart1', // name
    $title, // title
    $legend, // legend
    $plotArea, // plotArea
    true, // plotVisibleOnly
    DataSeries::EMPTY_AS_GAP, // displayBlanksAs
    null, // xAxisLabel
    $yAxisLabel  // yAxisLabel
);

// Set the position where the chart should appear in the worksheet
$chart->setTopLeftPosition('A7');
$chart->setBottomRightPosition('H20');

// Add the chart to the worksheet
$worksheet->addChart($chart);

I want to add gap between two bars. I can made the change in ms excel from format->series->series overlap option. In phpspreadsheet how can I achieve that. Thanks in advance