get only one category and its sub category in magento

In this category get a particular category and its sub category.
First of all load category ID and after check category have sub child or not then print with foreach loop.

Code here....
$categoryName = Mage::getModel('catalog/category')->load(236);
$subCategories = $category->getChildrenCategories();
if (count($subCategories) > 0){
    echo $categoryName->getName() . "<br>";
    foreach($subCategories as $subcat){
         echo $subcat->getName() . "<br>";