Parts explosion with repeated subtrees

Imagine that we have a forest of trees called "Menu" which stores the menu items for a restaurant. The first level under the root is the dishes served. Each dish is then decomposed into its ingredients; the ingredient can be either simple (salt, water, milk, flour, etc) or it can have a recipe of its own (Béarnaise sauce, Hollandaise sauce, etc.)

Let me build a tree of each dish or recipe down to its most basic simple ingredients:

CREATE TABLE Menu
(dish_name VARCHAR (25) NOT NULL,
 food_item VARCHAR (25) NOT NULL,
  item_type CHAR (6) NOT NULL DEFAULT ‘simple'

        CHECK (item_type IN (‘dish', ‘recipe', ‘simple')),  PRIMARY KEY (dish_name, food_item),
<< constraints >>);

INSERT INTO Menu
VALUES (‘Eggs Benedict', ‘English Muffin', ‘simple'),

(‘Eggs Benedict', ‘Canadian Bacon', ‘simple'),
(‘Eggs Benedict', ‘Egg', ‘simple'),
(‘Eggs Benedict', ‘Béarnaise sauce', ‘recipe');

INSERT INTO Menu
VALUES (‘Béarnaise sauce', ‘Dill', ‘simple'),

(‘Béarnaise sauce', ‘Hollandaise sauce', ‘recipe');

INSERT INTO Menu
VALUES (‘Hollandaise sauce', ‘Egg‘, ‘simple'),