Magento. Get categories by ID and display subcategories if any. Will work directly from top.phtml

gistfile1.txt

  	  <?php $_helper = Mage::helper('catalog/category');
			    $children = Mage::getModel('catalog/category')->getCategories(CATETGORY_ID_HERE);
			    foreach ($children as $category):
			        $category = Mage::getModel('catalog/category')->load($category->getId());
			        echo '<li class="level1"><a href="' . $category->getUrl() . '">' . $category->getName() . '</a>';
				        $category = Mage::getModel('catalog/category')->load($category->getId());
		                $_subcategories = $category->getChildrenCategories();
		                if (count($_subcategories) > 0): ?>
		                    <ul>
		                        <?php foreach($_subcategories as $_subcategory): ?>
		                            <li class="level2">
		                                <a href="<?php echo $_helper->getCategoryUrl($_subcategory) ?>">
		                                    <?php echo $_subcategory->getName() ?>
		                                </a>
		                            </li>
		                        <?php endforeach; ?>
		                    </ul>
		                <?php endif;
			        echo '</li>';
			    endforeach;
			?>