使用PHP中的amazon API列出root browsenodes（类别）和子browsenodes（子类别）

I'm using Amazon API in PHP.

I need to list the categories (root browsenodes) of products.

Ex. men fashion    women fashion     kitchen     baby&kids

For this couldn't find the solution.

The search function on products is working fine.

I have included these file for search products:
amazon_api_class.php , aws_signed_request.php

I'm using the following function to get search results

Filename: amazon_api_class.php

public function searchProducts($search, $category, $searchType = "UPC")
    {
        $allowedTypes = array("UPC", "TITLE", "ARTIST", "KEYWORD");
        $allowedCategories = array("Music", "DVD", "VideoGames", "Apparel", "Automotive", "Baby" ,"Beauty",  "Books",  
                "Classical",  "DigitalMusic",  "Electronics",  "HealthPersonalCare",  "HomeGarden",  "Industrial",  "Jewelry",  
                "Kitchen",  "Magazines",  "Miscellaneous",  "OfficeProducts",  "Video", "Watches");

        switch($searchType) 
        {
            case "UPC" :    $parameters = array("Operation"     => "ItemLookup",
                                                "ItemId"        => $search,
                                                "SearchIndex"   => $category,
                                                "IdType"        => "UPC",
                                                "ResponseGroup" => "Medium");
                            break;

            case "TITLE" :  $parameters = array("Operation"     => "ItemSearch",
                                                "Title"         => $search,
                                                "SearchIndex"   => $category,
                                                "ResponseGroup" => "Medium");
                            break;


        }


        $xml_response = $this->queryAmazon($parameters);


        return $this->verifyXmlResponse($xml_response);

    } 

Now i'm looking for a function like this which will give the available categories in xml response.