Magento display root categories and subcategories

<?php $_helper = Mage::helper('catalog/category') ?>
<?php $_categories = $_helper->getStoreCategories() ?>
<?php $currentCategory = Mage::registry('current_category') ?>
<?php if (count($_categories) > 0): ?>
    <ul>
    <?php foreach($_categories as $_category): ?>
    <li>
    <a href="<?php echo $_helper->getCategoryUrl($_category) ?>">
    <?php echo $_category->getName() ?> <!--//Top Level Category Listing-->
    </a>
    <?php $_category = Mage::getModel('catalog/category')->load($_category->getId()) ?>
    <?php $_subcategories = $_category->getChildrenCategories() ?>
    <?php if (count($_subcategories) > 0): ?>
    <ul>
    <?php foreach($_subcategories as $_subcategory): ?>
    <li>
    &nbsp;&nbsp;&nbsp;<a href="<?php echo $_helper->getCategoryUrl($_subcategory) ?>"> <!--//Sub Category Listing-->
    <?php echo $_subcategory->getName() ?>
    </a>
    </li>
    <?php endforeach; ?>
    </ul>
    <?php endif; ?>
    </li>
    <?php endforeach; ?>
    </ul>
<?php endif; ?>