How To Get Sub Categories in Magento ?`

Question

I am playing with magento's home page where I have created a tab Which Shows all the categories including Root, categories, and Sub Categories (In One Tab). Now I want to Show Only Main Categories( Whose Parent Is Root) in main Tab And under Each Category I want to List Their respective Sub Categories. I wrote The following Code to achieve a part of this,

MODEL CLASS

public function getsubCategory($parent)
{

    $subcategoryCollection = Mage::getModel('catalog/category')
    ->getCollection()
    ->addAttributeToFilter('parent_id', $parent);
       return $subcategoryCollection;

BLOCK CLASS

protected function b4Html_subcategory($parent)
{
    $catModel = Mage::getModel('Pragtech_Sweet/category');
    $mysubCategory = $catModel->getsubCategory($parent);
    $this->mysubCategory = $myCategory; 
    return $mysubCategory;
}

TEMPLATE FILE

$obj = new Pragtech_Sweet_Block_Category();
$collection = $obj->b4Html();
foreach ($collection as $category)
    {
    $name = $category->getName();
    $parent = $category->getParent_id();

    foreach ($obj->b4Html_subcategory($parent) as $subcategory)
    {   
       $subname = $subcategory->getName();
       //Here Will Go Ther Code For Sub Categories

    }

but it doesn't work.. I am unable to understand where I am doing wrong... Can anyone help me out

Solution

Do this instead :

Mage::getModel('catalog/category')->load('23')->getChildrenCategories();

and iterate over the result.

and that's how i found it out:

$object = Mage::getModel('catalog/category'); 
print_r(get_class_methods($object));
print_r($object->load('23')->getChildrenCategories()->toArray());