How to get the parent of a grouping in PHPExcel?

Question

PHP

I am using the PHPExcel library.
The .xlsx structure is shown in the photo

. I use the following code:

// Подключаю библиотеку
require_once ($_SERVER['DOCUMENT_ROOT'].'Classes/PHPExcel.php');
$pExcel = PHPExcel_IOFactory::load($_SERVER['DOCUMENT_ROOT'].'/out.xlsm');
foreach ($pExcel->getWorksheetIterator() as $worksheet) {
    foreach ($worksheet->getRowDimensions() as $rowDimension) {
        $level = $rowDimension->getOutlineLevel();
        echo  '<pre>';
        print_r($level);
        echo  '</pre>';
}
}

The $level variable stores the nesting level of the grouping. And how to get the name of the group's parent?