TYPO3 Core

Having:

'config' => array(
        'type' => 'select',
        'size' => 10,
        'foreign_table' => 'pages',
        'MM' => 'tx_tcshop_product_mm',
        'MM_insert_fields' => array('ident' => 'category'),
        'MM_match_fields' => array('ident' => 'category'),
        'maxitems' => 9999,
        'minitems' => 0,
        'renderMode' => 'tree',
        'treeConfig' => array(
            'expandAll' => 1,
            'parentField' => 'pid',
            'rootUid' => ??????,
            'maxLevels' => 5,
            'appearance' => array(
                'showHeader' => TRUE,
                'nonSelectableLevels' => 0',                
            ),
        ),
    ),

The rootUid = ?????, how should we be able to substitute by TSconfig when the core (sysext/core/Classes/Tree/TableConfiguration/TreeDataProviderFactory.php) says:

$treeConfiguration = $tcaConfiguration['treeConfig'];
if (isset($treeConfiguration['rootUid'])) {
        $dataProvider->setRootUid(intval($treeConfiguration['rootUid']));
}