Дерево подразделов в Битриксе

$iblock = 3;
 $res = CIBlockSection::GetList(
 Array("LEFT_MARGIN" => "ASC"),
 Array("IBLOCK_ID" => $iblock, "ACTIVE" => "Y", "GLOBAL_ACTIVE" => "Y"),
 true,
 Array("ID", "NAME", "DESCRIPTION", "PICTURE","SECTION_PAGE_URL")
 );

 while ($arSection = $res->GetNext()) {
$iCnt2 = CIBlockElement::GetList(array(), array("IBLOCK_ID" => $iblock, "ACTIVE" => "Y", "SECTION_ID" => $arSection['ID']), array());
 if ($iCnt2 == 0) {
 echo '<b><a href="' . $arSection['SECTION_PAGE_URL'] .'">' .$arSection['NAME'] . "</a></b><br>";
 continue;
 }
echo '<ul><b><a href="' . $arSection['SECTION_PAGE_URL'] .'">' .$arSection['NAME'] . "</a></b><br>";
 $arSelect = Array("ID", "NAME", "DATE_ACTIVE_FROM");
 $iCnt = CIBlockElement::GetList(array(), array("IBLOCK_ID" => $iblock, "ACTIVE" => "Y", "SECTION_ID" => $arSection['ID']), false, Array(), $arSelect);

 while ($ob = $iCnt->GetNextElement()) {
 $arFields = $ob->GetFields();
foreach ($arResult['ITEMS'] as $cell => $arElement) {
 if ($arFields['ID'] == $arElement['ID']) {
 echo '<li><a href="' . $arElement['DETAIL_PAGE_URL'] .'">' . $arElement['NAME'] . "</a></li>";
 }
 }
 }
 echo "</ul>";
 }