How to getch all root categories and its subcategories in magento?

$intRootCategoryId = Mage::app()->getStore()->getRootCategoryId();
$objParentCategories = Mage::getModel('catalog/category')->getCollection()->addAttributeToFilter('parent_id',$intRootCategoryId)->addAttributeToFilter('is_active',1)->setOrder('position','ASC');
foreach($objParentCategories as $objSpecParentCategory)
{                                                          
    $objFinalCategory = Mage::getModel('catalog/category')->load($objSpecParentCategory->getId());
    $objSubCategories = Mage::getModel('catalog/category')->getCollection()->addAttributeToFilter('parent_id',$objSpecParentCategory->getId())->addAttributeToFilter('is_active',1)->setOrder('position','ASC');
   
    if ($objSubCategories->count())
    {
        foreach($objSubCategories as $objSpecSubCategory)
        {
            $objFinalSubCategory = Mage::getModel('catalog/category')->load($objSpecSubCategory->getId());
            $objFinalSubCategory->getUrl();
            $objFinalSubCategory->getName();
        }   
    }
}