Amazon-ecs如何获得该产品的顶级类别？

I'm using the amazon-ecs gem to get product details from Amazon, using the itemlookup function (passing the ASIN). While I'm able to get all product details from this function, I'm not sure how to get the product's top level category - for example, if I have a children's book, I want the category as 'book' not fiction or children's book etc. I'm using the amazon-ecs gem to get product det