Generate Category Tree in Magento

<?php

$rootDir = ""; //include root path

include($rootDir."app/Mage.php");

$rootcatId= Mage::app()->getStore()->getRootCategoryId();

$categories = Mage::getModel('catalog/category')->getCategories($rootcatId);

function  get_categories($categories) {

    $array= '<ul>';

    foreach($categories as $category) {

        $cat = Mage::getModel('catalog/category')->load($category->getId());

        $count = $cat->getProductCount();

        $array .= '<li>'.

        '<a href="' . Mage::getUrl($cat->getUrlPath()). '">' .

                  $category->getName() . "(".$count.")</a>\n";

        if($category->hasChildren()) {

            $children = Mage::getModel('catalog/category')->getCategories($category->getId());

             $array .=  get_categories($children);

            }

         $array .= '</li>';

    }

    return  $array . '</ul>';

}

echo  get_categories($categories); ?>