private function writeBubbles($plotSeriesValues, $objWriter, PHPExcel_Worksheet $pSheet)
    {
        if (is_null($plotSeriesValues)) {
            return;
        }

        $objWriter->startElement('c:bubbleSize');
        $objWriter->startElement('c:numLit');

        $objWriter->startElement('c:formatCode');
        $objWriter->writeRawData('General');
        $objWriter->endElement();

        $objWriter->startElement('c:ptCount');
        $objWriter->writeAttribute('val', $plotSeriesValues->getPointCount());
        $objWriter->endElement();

        $dataValues = $plotSeriesValues->getDataValues();
        if (!empty($dataValues)) {
            if (is_array($dataValues)) {
                foreach ($dataValues as $plotSeriesKey => $plotSeriesValue) {
                    $objWriter->startElement('c:pt');
                    $objWriter->writeAttribute('idx', $plotSeriesKey);
                    $objWriter->startElement('c:v');
                    $objWriter->writeRawData(1);
                    $objWriter->endElement();
                    $objWriter->endElement();
                }
            }
        }

        $objWriter->endElement();
        $objWriter->endElement();

        $objWriter->startElement('c:bubble3D');
        $objWriter->writeAttribute('val', 0);
        $objWriter->endElement();
    }