Craft\ImageResizerService::getAssetFolders PHP Method

    public function getAssetFolders($tree, &$folderOptions)
    {
        foreach ($tree as $folder) {
            $folderOptions[] = array('label' => $folder->name, 'value' => $folder->id);
            $children = $folder->getChildren();
            if ($children) {
                $this->getAssetFolders($children, $folderOptions);
            }
        }
    }