bluec

<?php

define('MAGENTO', realpath(dirname(__FILE__)));
require_once MAGENTO . '/app/Mage.php';
Mage::app();

$category = Mage::getModel('catalog/category');
$tree = $category->getTreeModel();
$tree->load();

haruair

<?php
// Usually, you can get category tree from category helper
$helper = Mage::helper('catalog/category');
$nodes = $helper->getStoreCategories();
// return Varien_Data_Tree_Node_Collection
//        via Mage_Catalog_Model_Resource_Category


// However, this get method return active category only.
// Most of the samples are for collection of the category.