Subcategories in php

Hi, I have been trying to do this for weeks but i just cant figure this out. I have categories that have subcategories and i want to insert them into database. My table looks like this: cat_id, parent_id and cat_name. Let's say i wanna insert a subcategory that is associated with its parent category. For example ParentCat 1 ParentCat 1 > ItsSubCat 1 ParentCat 1 > ItsSubCat 2 ParentCat 1 > ItsSubCat 3 ParentCat 1 > ItsSubCat 4 ParentCat 2 ParentCat 2 > ItsSubCat 1 and so on ... I don't know how to create the script that inserts any subcategory(in this case let's say ItsSubCat 3) in its parent category. Please, can someone help me thanks