private function createAndPersistCategory($label, $parentCategory = null)
 {
     $this->categoriesCount++;
     $category = new Category();
     $category->setLabel($label)->setParentCategory($parentCategory);
     $this->manager->persist($category);
     $this->setReference(sprintf('category_%s', $this->categoriesCount), $category);
     return $category;
 }