Create category tree in Magento

setup.php

<?php
    $tree = array(
        'Category A' => array(
            'Category A-B' => array(
                'Category A-B-A',
                'Category A-B-B'
            ),
            'Category A-C' => array(
                'Category A-C-A',
                'Category A-C-B'
            ),
            'Category A-D',
        ),
        'Category B' => array(
            'Category B-B' => array(
                'Category B-B-A',
                'Category B-B-B'
            ),
            'Category B-C' => array(
                'Category B-C-A',
                'Category B-C-B'
            ),
        )
    );
    Mage::getModel('namespace_model/setup')->setCategoryTree($tree)->setupCategories();
?>

setup_model.php

<?php
class Namespace_Module_Model_Setup extends Mage_Core_Model_Abstract
{

    /**
     * Category tree for initial setup
     *
     * @var array
     */
    protected $_categories = array();

    /**
     * Set category tree to create
     *
     * @param array $tree
     * @return Namespace_Module_Model_Setup
     */
    public function setCategoryTree($tree)
    {
        $this->_categories = $tree;
        return $this;
    }

    /**
     * Setup categories based on set category tree
     *
     * @return Namespace_Module_Model_Setup
     */
    public function setupCategories()
    {
        foreach ($this->_categories as $categoryName => $categoryTree) {
            $this->_createCategories($categoryName, $categoryTree);
        }

        return $this;
    }

    /**
     * Create categories recursively
     *
     * @param string $categoryName
     * @param array|null $categoryTree
     * @param int $parentId
     * @return Namespace_Module_Model_Setup
     */
    protected function _createCategories($categoryName, $categoryTree = null, $parentId = 2)
    {
        $category = Mage::getModel('catalog/category');
        $parent = Mage::getModel('catalog/category')->load($parentId);
        $category->setStoreId(Mage_Core_Model_App::ADMIN_STORE_ID)
            ->setName($categoryName)
            ->setParentId($parentId)
            ->setPath($parent->getPath())
            ->setIsActive(1)
            ->setIsAnchor(1)
            ->save();

        if ($categoryTree && is_array($categoryTree)) {
            foreach ($categoryTree as $subCategoryName => $subCategoryTree) {
                if (!is_array($subCategoryTree)) {
                    $subCategoryName = $subCategoryTree;
                }
                $this->_createCategories($subCategoryName, $subCategoryTree, $category->getId());
            }
        }

        return $this;
    }
}
?>