search for: all_associated_product

hi, I''ve a normal Category model implemented with acts_as_tree (name, parent_id) that has_many :products (name, category_id). What I''m asking for is a method to fetch every product that belongs fall into a particular category and its children, eg: if I''m asking for a root node (/category/show/1) I need to display every product that have category_id = 1 AND every product