There is a table that contains data about a set of folders. Each folder can be a child of another. If folder_id is null, then it's a root level folder.
If folder_id is a number, it is a child of the folder with that number.
| id | name | folder_id |
|---|---|---|
| 1 | images | null |
| 2 | css | null |
| 3 | home | 1 |