Add a tree like left menu in Magento.

Magento in common has no left menu.
So i edit some core and design code to implement a left tree like menu.
Here i give the example of my code.
Step 1:Edit core code in app/code/core/mage/catalog/Block/Navigation.php and add these code in LeftNav.php in same place

<?php
/**
 * Magento
 *
 * NOTICE OF LICENSE
 *
 * This source file is subject to the Open Software License (OSL 3.0)
 * that is bundled with this package in the file LICENSE.txt.
 * It is also available through the world-wide-web at this URL:
 * http://opensource.org/licenses/osl-3.0.php
 * If you did not receive a copy of the license and are unable to
 * obtain it through the world-wide-web, please send an email
 * to license@magentocommerce.com so we can send you a copy immediately.
 *
 * DISCLAIMER
 *
 * Do not edit or add to this file if you wish to upgrade Magento to newer
 * versions in the future. If you wish to customize Magento for your
 * needs please refer to http://www.magentocommerce.com for more information.
 *
 * @category   Mage
 * @package    Mage_Catalog
 * @copyright  Copyright (c) 2008 Irubin Consulting Inc. DBA Varien (http://www.varien.com)
 * @license    http://opensource.org/licenses/osl-3.0.php  Open Software License (OSL 3.0)
 */

/**
 * Catalog navigation
 *
 * @category   Mage
 * @package    Mage_Catalog
 * @author      Magento Core Team <core@magentocommerce.com>
 */
class Mage_Catalog_Block_LeftNav extends Mage_Core_Block_Template
{
    protected $_categoryInstance = null;

    protected function _construct()
    {
        $this->addData(array(
            'cache_lifetime'    => false,
            'cache_tags'        => array(Mage_Catalog_Model_Category::CACHE_TAG, Mage_Core_Model_Store_Group::CACHE_TAG),
        ));
    }

    /**
     * Retrieve Key for caching block content
     *
     * @return string
     */
    public function getCacheKey()
    {
        return 'CATALOG_NAVIGATION_' . Mage::app()->getStore()->getId()
            . '_' . Mage::getDesign()->getPackageName()
            . '_' . Mage::getDesign()->getTheme('template')
            . '_' . Mage::getSingleton('customer/session')->getCustomerGroupId()
            . '_' . md5($this->getTemplate() . $this->getCurrenCategoryKey());
    }

    public function getCurrenCategoryKey()
    {
        if ($category = Mage::registry('current_category')) {
            return $category->getPath();
        } else {
            return Mage::app()->getStore()->getRootCategoryId();
        }
    }

    /**
     * Get catagories of current store
     *
     * @return Varien_Data_Tree_Node_Collection
     */
    public function getStoreCategories()
    {
        $helper = Mage::helper('catalog/category');
        return $helper->getStoreCategories();
    }

    /**
     * Retrieve child categories of current category
     *
     * @return Varien_Data_Tree_Node_Collection
     */
    public function getCurrentChildCategories()
    {
        $layer = Mage::getSingleton('catalog/layer');
        $category   = $layer->getCurrentCategory();
        /* @var $category Mage_Catalog_Model_Category */
        $categories = $category->getChildrenCategories();
        $productCollection = Mage::getResourceModel('catalog/product_collection');
        $layer->prepareProductCollection($productCollection);
        $productCollection->addCountToCategories($categories);
        return $categories;
    }

    /**
     * Checkin activity of category
     *
     * @param   Varien_Object $category
     * @return  bool
     */
    public function isCategoryActive($category)
    {
        if ($this->getCurrentCategory()) {
            return in_array($category->getId(), $this->getCurrentCategory()->getPathIds());
        }
        return false;
    }

    protected function _getCategoryInstance()
    {
        if (is_null($this->_categoryInstance)) {
            $this->_categoryInstance = Mage::getModel('catalog/category');
        }
        return $this->_categoryInstance;
    }

    /**
     * Get url for category data
     *
     * @param Mage_Catalog_Model_Category $category
     * @return string
     */
    public function getCategoryUrl($category)
    {
        if ($category instanceof Mage_Catalog_Model_Category) {
            $url = $category->getUrl();
        } else {
            $url = $this->_getCategoryInstance()
                ->setData($category->getData())
                ->getUrl();
        }

        return $url;
    }

    /**
     * Enter description here...
     *
     * @param Mage_Catalog_Model_Category $category
     * @param int $level
     * @param boolean $last
     * @return string
     */
    public function drawItem($category, $level=0, $last=false)
    {
        $html = '';
        if (!$category->getIsActive()) {
            return $html;
        }
        if (Mage::helper('catalog/category_flat')->isEnabled()) {
            $children = $category->getChildrenNodes();
            $childrenCount = count($children);
        } else {
            $children = $category->getChildren();
            $childrenCount = $children->count();
        }
        $hasChildren = $children && $childrenCount;
        $html.= '<li';
        if ($hasChildren) {
             //$html.= ' onmouseover="toggleMenu(this,1)" onmouseout="toggleMenu(this,0)"';
   //replace
   $html.= '';
        }

       // $html.= ' class="level'.$level;
       // $html.= ' nav-'.str_replace('/', '-', Mage::helper('catalog/category')->getCategoryUrlPath($category->getRequestPath()));
        if ($this->isCategoryActive($category)) {
           // $html.= ' active';
      $html .='';
        }
        if ($last) {
           // $html .= ' last';
      $html .='';
        }
        if ($hasChildren) {
            $cnt = 0;
            foreach ($children as $child) {
                if ($child->getIsActive()) {
                    $cnt++;
                }
            }
            if ($cnt > 0) {
              //  $html .= ' parent';
      //$html .=' current';
      $html .='';
            }
        }
        $html.= '>'."\n";
        $html.= '<a href="'.$this->getCategoryUrl($category).'"><span>'.$this->htmlEscape($category->getName()).'</span></a>'."\n";

        if ($hasChildren){

            $j = 0;
            $htmlChildren = '';
            foreach ($children as $child) {
                if ($child->getIsActive()) {
                    $htmlChildren.= $this->drawItem($child, $level+1, ++$j >= $cnt);
                }
            }

            if (!empty($htmlChildren)) {
                $html.= '<ul>'."\n"
                        .$htmlChildren
                        .'</ul>';
            }

        }
        $html.= '</li>'."\n";
        return $html;
    }

    /**
     * Enter description here...
     *
     * @return Mage_Catalog_Model_Category
     */
    public function getCurrentCategory()
    {
        if (Mage::getSingleton('catalog/layer')) {
            return Mage::getSingleton('catalog/layer')->getCurrentCategory();
        }
        return false;
    }

    /**
     * Enter description here...
     *
     * @return string
     */
    public function getCurrentCategoryPath()
    {
        if ($this->getCurrentCategory()) {
            return explode(',', $this->getCurrentCategory()->getPathInStore());
        }
        return array();
    }

    /**
     * Enter description here...
     *
     * @param Mage_Catalog_Model_Category $category
     * @return string
     */
    public function drawOpenCategoryItem($category) {
        $html = '';
        if (!$category->getIsActive()) {
            return $html;
        }

        $html.= '<li';

        if ($this->isCategoryActive($category)) {
            $html.= ' class="active"';
        }

        $html.= '>'."\n";
        $html.= '<a href="'.$this->getCategoryUrl($category).'"><span>'.$this->htmlEscape($category->getName()).'</span></a>'."\n";

        if (in_array($category->getId(), $this->getCurrentCategoryPath())){
            $children = $category->getChildren();
            $hasChildren = $children && $children->count();

            if ($hasChildren) {
                $htmlChildren = '';
                foreach ($children as $child) {
                    $htmlChildren.= $this->drawOpenCategoryItem($child);
                }

                if (!empty($htmlChildren)) {
                    $html.= '<ul>'."\n"
                            .$htmlChildren
                            .'</ul>';
                }
            }
        }
        $html.= '</li>'."\n";
        return $html;
    }

}