limit number of categories of a page php

I have a php function that shows the categories registered in the database, but I would like to limit the number of categories that appear, see the code

if ($output!='') {
                // @todo ul here is hacky but front end templates are limited, fix this when possible
                $output = '<ul>'.$output.'</ul>';
}
return $output;

I wanted to maybe limit within the ul type for 10 categories at most

Complete code:

<?php

CLASS ISC_DEPARTAMENTOS_PANEL extends PANEL
{
    public function SetPanelSettings()
    {
        if (ISC_CATEGORY::areCategoryFlyoutsEnabled()) {
            $GLOBALS['SideCategoryListTypeClass'] = 'SideCategoryListFlyout';
            $output = $this->_generateFlyoutOutput();
        } else {
            $GLOBALS['SideCategoryListTypeClass'] = 'SideCategoryListClassic';
            $output = $this->_generateClassicOutput();
        }

        if (!$output) {
            $this->DontDisplay = true;
            return;
        }

    $GLOBALS['SNIPPETS']['departamentos'] = $output;
}

/**
* get the html for sub category list
*
* @param array $categories the array of all categories in a tree structure
* @param int $parentCatId the parent category ID of the sub category list
*
* return string the html of the sub category list
*/
protected function _getSubCategory($categories, $parentCatId)
{

    $output = '';
    //if there is sub category for this parent cat
    if (isset($categories[$parentCatId]) && !empty($categories[$parentCatId])) {
        $i=1;
        foreach ($categories[$parentCatId] as $subCat) {
            // If we don't have permission to view this category then skip
            if (!CustomerGroupHasAccessToCategory($subCat['categoryid'])) {
                continue;
            }
            $catLink = CatLink($subCat['categoryid'], $subCat['catname'], false);
            $catName = isc_html_escape($subCat['catname']);

            $GLOBALS['SubCategoryList'] = $this->_getSubCategory($categories, $subCat['categoryid']);

            //set the class for the last category of its parent category
            $GLOBALS['LastChildClass']='';
            if($i == count($categories[$parentCatId])) {
                $GLOBALS['LastChildClass']='LastChild';
            }
            $i++;

            $GLOBALS['CategoryName'] = $catName;
            $GLOBALS['CategoryLink'] = $catLink;
            $output .= $GLOBALS['ISC_CLASS_TEMPLATE']->GetSnippet("SideCategoryList");
        }
    }
    if ($output!='') {
        // @todo ul here is hacky but front end templates are limited, fix this when possible
        $output = '<ul>'.$output.'</ul>';
    }
    return $output;
}

/**
 * This method creates and returns front-end output for original, non-flyout-enabled category menus
 *
 * @return string
 */
protected function _generateClassicOutput ()
{
    $output = "";
    $categories = $GLOBALS['ISC_CLASS_DATA_STORE']->Read('RootCategories');

    if (!isset($categories[0])) {
        return $output;
    }

    foreach($categories[0] as $rootCat) {
        // If we don't have permission to view this category then skip
        if(!CustomerGroupHasAccessToCategory($rootCat['categoryid'])) {
            continue;
        }

        $GLOBALS['SubCategoryList'] = $this->_getSubCategory($categories, $rootCat['categoryid']);
        $GLOBALS['LastChildClass']='';
        $GLOBALS['CategoryName'] = isc_html_escape($rootCat['catname']);
        $GLOBALS['CategoryLink'] = CatLink($rootCat['categoryid'], $rootCat['catname'], true);
        // @todo ul here is hacky but front end templates are limited, fix this when possible
        $output .= $GLOBALS['ISC_CLASS_TEMPLATE']->GetSnippet("SideCategoryList");
    }

    return $output;
}

/**
 * This method creates and returns front-end output for flyout-enabled category menus
 *
 * @return string
 */
protected function _generateFlyoutOutput ()
{
    $categories = new ISC_SITEMAP_MODEL_CATEGORIES;
    $categories->setMaximumDepth((int)GetConfig('CategoryListDepth') - 1);
    $categories = $categories->getTree();

    $renderer = new Store_SiteMap_Renderer;
    return $renderer->setSiteMapTree($categories)
        ->setRootClasses('sf-menu sf-vertical')
        ->render();
}
}