$IBLOCK_ID = 79;
$arFilter = Array(
'IBLOCK_ID'=>$IBLOCK_ID,
'GLOBAL_ACTIVE'=>'Y');
$obSection = CIBlockSection::GetTreeList($arFilter);
while($arResult = $obSection->GetNext()){
for($i=0;$i<=($arResult['DEPTH_LEVEL']-2);$i++)
echo "..";
echo $arResult['NAME'].'<br>';
}