display all subcategory of main category in magento

 <?php

 $root_category = Mage::getModel('catalog/category')->load(3);  

// Put your root category ID here.

 
$subcategories = $root_category->getChildren();
foreach(explode(',',$subcategories) as $subcategory) {
$category = Mage::getModel('catalog/category')->load($subcategory);
echo '<a href="'.$category->getURL() .'" />'.$category->getName().'</a><br/>';
  }

  ?>

 Particular Category And Subcategory Not Show in  Category Menu:--

 <h3>Category</h3>
 <?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 $_category): ?>
            <li>
   <?php if (!in_array($_category->getId(), array(10))) : ?>
                <a href="<?php echo $_helper->getCategoryUrl($_category) ?>">
                    <?php echo $_category->getName() ?>
                </a>
    <?php endif; ?>
                <?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>
                                <a href="<?php echo $_helper->getCategoryUrl($_subcategory) ?>">
                                    <?php echo $_subcategory->getName() ?>
                                </a>
                            </li>
                        <?php endforeach; ?>
                    </ul>
                <?php endif; ?>
            </li>
        <?php endforeach; ?>
  
    </ul>
<?php endif; ?>