How to get nested directory structure into array or database?

Question

I'm making a "photo uploader" project that can get all sub-files and sub-directory of specific folder.
I've used iterator to get files and directory :

$path = dirname(__FILE__).'/';

use RecursiveIteratorIterator as RII;
use RecursiveDirectoryIterator as RDI;
use RecursiveCallbackFilterIterator as RCFI;

$directory = new RDI($path, RDI::SKIP_DOTS);

$filter = new RCFI($directory, function ($current, $key, $iterator) {
    return $current->isDir() || preg_match('/^.+(.jpe?g|.png|.gif)$/i', $current->getPathname()) > 0;
});
$iterator = new RII($filter, RII::SELF_FIRST);

After got them, I want their structure be store into database, into the following table :
column `id` is AUTO_INCREMENT

table `item`
| id | title | type | parent_id |

Like Unix, everything is file, even dir, I use column type to store folder or file, so I can use only one table.
For example, I got two files and two folder :

test (folder)
 -file1.png
 -subtest (folder)
  --file2.png

And I want to store them like this (just for example, the order of them is not important) :

| id |   title   |   type   | parent_id |
-----------------------------------------
| 1  |   test    |  folder  |    null   |
| 2  | file1.png |   file   |     1     |
| 3  |  subtest  |  folder  |     1     |
| 4  | file2.png |   file   |     3     |

I know how to get I don't know how to get every folder and their parent folder structure into array, then store them into table like above

Answer 1

Finally, I got a solution (Thanks u/colshrapnel) :
The easiest way would be to maintain a directory map manually. Say, after inserting the test directory you will get the id and store the full path in the array, $map[$current->getPathname()] = 1; and so on. Once getting a new entry, get the dirname($current->getPathname()) and test it against the map to get the parent id

Hence the test/subtest should give you 3