Display Categories and SubCategories in Magento

First Put Xml in catalog.xml

 <reference name="left">

<block type="catalog/navigation" name="catalog.category" template="catalog/category/list_category.phtml"/>

 </reference>

and make a file list_category.phtml. path is->

app\design\frontend\base\default\template\catalog\category\list_category.phtml

and put below given code.
           

 Display Top Level Categories Only 

<?php $_helper = Mage::helper('catalog/category') ?>

<?php $_categories = $_helper->getStoreCategories() ?>

<?php if (count($_categories) > 0): ?>

    <ul>

        <?php foreach($_categories as $_category): ?>

            <li>

                <a href="<?php echo $_helper->getCategoryUrl($_category) ?>">

                    <?php echo $_category->getName() ?>

                </a>

            </li>

        <?php endforeach; ?>

    </ul>

<?php endif; ?>

*******************************************************************************

Display Top Level Categories and ALL 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() ?>

                </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>

                                <a href="<?php echo $_helper->getCategoryUrl($_subcategory) ?>">

                                    <?php echo $_subcategory->getName() ?>

                                </a>

                            </li>

                        <?php endforeach; ?>

                    </ul>

                <?php endif; ?>

            </li>

        <?php endforeach; ?>

    </ul>

<?php endif; ?>

Display Top Level Categories and Current Categories SubCategories

<?php foreach ($this->getStoreCategories() as $_category): ?>
<li>
<a href="<?php echo $this->getCategoryUrl($_category) ?>"><?php echo $this->htmlEscape($_category->getName()) ?></a>
<?php
$_catid=$_category->getId();
$category = Mage::getModel('catalog/category')->load($_catid);
$subcategory = $category->getAllChildren(true);
array_shift($subcategory);
if($subcategory!=null)
{?>
<ul>
<?php
foreach ($subcategory as $sub)
{
$sub1 = Mage::getModel('catalog/category')->load( $sub);
?>
<li><a href="<?php echo $sub1->getUrl();?>"><span>
<?php echo $sub1->getName(); ?>
</span></a></li>
<?php } ?>

</ul>
<?php }?>

</li>
<?php endforeach ?>