public function load()
    {
        if ($this->_isCollectionLoaded == false) {


            $collection = Mage::getResourceModel('catalog/category_collection')->addNameToResult();
            /* @var $collection Mage_Catalog_Model_Resource_Eav_Mysql4_Category_Collection */

            foreach ($collection as $category) {
                /** @var $category Mage_Catalog_Model_Category */
                $structure = explode('/', $category->getPath());
                $pathSize = count($structure);
                if ($pathSize > 1) {
                    $path = array();
                    for ($i = 1; $i < $pathSize; $i++) {
                        $path[] = $collection->getItemById($structure[$i])->getName();
                    }
                    $rootCategoryName = array_shift($path);
                    if (!isset($this->_categoriesWithRoots[$rootCategoryName])) {
                        $this->_categoriesWithRoots[$rootCategoryName] = array();
                    }
                    $index = $this->_implodeEscaped('/', $path);

                    $this->_categoriesWithRoots[$rootCategoryName][$index] = array(
                        'entity_id' => $category->getId(),
                        'path' => $category->getPath(),
                        'level' => $category->getLevel(),
                        'position' => $category->getPosition()
                    );

//allow importing by ids.
                    if (!isset($this->_categoriesWithRoots[$structure[1]])) {
                        $this->_categoriesWithRoots[$structure[1]] = array();
                    }
                    $this->_categoriesWithRoots[$structure[1]][$category->getId()] =
                        $this->_categoriesWithRoots[$rootCategoryName][$index];
                }
            }


            $collection = clone $this->_categoryCollection;
            $collection->removeAttributeToSelect();
            $tableName = $collection->getResource()->getEntityTable();
            $collection->getSelect()->from($tableName, ['entity_id', 'website_id', 'email']);

            $this->_byPagesIterator->iterate(
                $this->_categoryCollection,
                $this->_pageSize,
                [[$this, 'addCustomer']]
            );

            $this->_isCollectionLoaded = true;
        }
    }