How to get all subcategories of a category in Magento

 >> Suppose you need to get the list of all subcategory of "cat1" (id : 10)

    <?php
       $category = Mage::getModel('catalog/category')->load(10); // load the parent category
    ?>
    There are many way to do it. I'll show you the two :
   
    1. $subcatCollection = Mage::getModel('catalog/category')->getCollection()
                ->addAttributeToSelect('*')
                ->addAttributeToFilter('is_active','1')
                ->addAttributeToFilter('parent_id',array('eq' => 10));
               
       // This will return the subcategory collection.
               
   2. $subcategories = $category->getChildren();
   
       // This will return all subcategory id with comma separator like : 11,12,13