How to get All Sub Category in Magento using Parent Category Id ?

<?php
require_once 'app/Mage.php';
set_time_limit(0);
error_reporting(E_ALL);
ini_set('display_errors', 1);
ini_set('memory_limit', '1024M');
ini_set('max_execution_time', 12000);
Mage::app();
Mage::app()->getStore()->setId(Mage_Core_Model_App::ADMIN_STORE_ID);


?>
<?php $_helper = Mage::helper('catalog/category') ?>
<?php $categoryId = 12449;?>
<?php $category = Mage::getModel('catalog/category')->load($categoryId) ?>
<?php $_categories = $category->getChildrenCategories() ?>

<?php if (count($_categories) > 0): ?>
    <ul>
        <?php foreach($_categories as $_category): ?>
            <li>
                <a href="<?php echo $_helper->getCategoryUrl($_category) ?>"><?php echo $_category->getName() ?></a>
                <?php $_category = Mage::getModel('catalog/category')->load($_category->getId()) ?>
                <?php if($_category->hasChildren()):?>
                <?php $_subcategories = $_category->getChildrenCategories() ?>
                    <ul>
                        <?php foreach($_subcategories as $_subcategory): ?>
                            <li>
                                <a href="<?php echo $_helper->getCategoryUrl($_subcategory) ?>"><?php echo $_subcategory->getName() ?></a>
                                <?php $_category2 = Mage::getModel('catalog/category')->load($_subcategory->getId()) ?>
                                <?php if($_category2->hasChildren()):?>
                                <?php $_subcategories2 = $_category2->getChildrenCategories() ?>
                                    <ul>
                                        <?php foreach($_subcategories2 as $_subcategory2): ?>
                                            <li>
                                                <a href="<?php echo $_helper->getCategoryUrl($_subcategory2) ?>"><?php echo $_subcategory2->getName() ?></a>
                                            </li>
                                        <?php endforeach; ?>
                                    </ul>
                                <?php endif; ?>

                            </li>
                        <?php endforeach; ?>
                    </ul>
                <?php endif; ?>
            </li>
        <?php endforeach; ?>
    </ul>
<?php endif; ?>


Second Method 

$category_ids = array();
$catID = 12449;

function retrieveAllChilds($id = null, $childs = null) {
    $category = Mage::getModel('catalog/category')->load($id);
    $subCategory = $category->getResource()->getChildren($category, true);

foreach ($subCategory as $categoryID)
{
$sCategory = Mage::getModel('catalog/category')->load($categoryID);
//$catnames = array();
//$category_ids = array();
foreach ($sCategory->getParentCategories() as $parent) {
//$catnames[] = $parent->getName();
//array_push($category_ids,$parent->getName());
$category_ids[$parent->getId()] = $parent->getName();
}
//echo  implode('->',$catnames);
//echo '<br>';
/*echo "<pre>";
print_r($category_ids);*/

}
return $category_ids;
}

$dd = retrieveAllChilds(12449);

echo "<pre>";
print_r($dd);