Contao\DC_Table::ajaxTreeView PHP Method

    public function ajaxTreeView($id, $level)
    {
        if (!\Environment::get('isAjaxRequest')) {
            return '';
        }
        $return = '';
        $table = $this->strTable;
        $blnPtable = false;
        // Load parent table
        if ($GLOBALS['TL_DCA'][$this->strTable]['list']['sorting']['mode'] == 6) {
            $table = $this->ptable;
            \System::loadLanguageFile($table);
            $this->loadDataContainer($table);
            $blnPtable = true;
        }
        $blnProtected = false;
        // Check protected pages
        if ($table == 'tl_page') {
            $objParent = \PageModel::findWithDetails($id);
            $blnProtected = $objParent->protected ? true : false;
        }
        $margin = $level * 20;
        $hasSorting = $this->Database->fieldExists('sorting', $table);
        $arrIds = array();
        // Get records
        $objRows = $this->Database->prepare("SELECT id FROM " . $table . " WHERE pid=?" . ($hasSorting ? " ORDER BY sorting" : ""))->execute($id);
        while ($objRows->next()) {
            $arrIds[] = $objRows->id;
        }
        /** @var SessionInterface $objSession */
        $objSession = \System::getContainer()->get('session');
        $blnClipboard = false;
        $arrClipboard = $objSession->get('CLIPBOARD');
        // Check clipboard
        if (!empty($arrClipboard[$this->strTable])) {
            $blnClipboard = true;
            $arrClipboard = $arrClipboard[$this->strTable];
        }
        for ($i = 0, $c = count($arrIds); $i < $c; $i++) {
            $return .= ' ' . trim($this->generateTree($table, $arrIds[$i], array('p' => $arrIds[$i - 1], 'n' => $arrIds[$i + 1]), $hasSorting, $margin, $blnClipboard ? $arrClipboard : false, $id == $arrClipboard['id'] || is_array($arrClipboard['id']) && in_array($id, $arrClipboard['id']) || !$blnPtable && !is_array($arrClipboard['id']) && in_array($id, $this->Database->getChildRecords($arrClipboard['id'], $table)), $blnProtected));
        }
        return $return;
    }