Related lists

we need to have an option when options available for selection from one list is limited with another one example: I have two-level classification like:

• fruits: -- apples -- pineapples
• vegetables: -- potato -- carrot

and I have two controls: "type of food" and "exact choice". so when I select "fruits" in first one I'm able to select apples and not able to select potato in second one

also there's a question how better organize lists:

• "id - name - parrent id"
• three lists: two with details and one with relations
• have a one big list with all combinations