how to list what is inside a directory using PHP?

Dear Experts,
I use PHP 7 and Linux server
I want to list all the folders and files inside a directory

I want to list it like this:

firstfolder
      file1.jpg
      file2.jpg
      file3.jpg
secondefolder
      filename.jpg
      filename2.jpg

How can I do that with PHP?

below code works perfectly fine. However it only brings me one folder, I want to see nested folders and what is inside..

$handle = opendir(dirname(realpath('myfolder')).'/myfolder/1234/');
        while($file = readdir($handle)){
            if($file !== '.' && $file !== '..'){
                echo '<img src="myfolder/1234/'.$file.'" border="0" />';
            }
 }

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thank you