Great thanks, that did the job with the SimpleTreeDropdownField. Brilliant!
Regarding the last thing, I've done this to remove the extended options from folders and it works:
public function updateCMSFields(FieldSet &$fields) {
if ($this->ClassName == "image")
{
$fields->push(new DropdownField('Kategori','Kategori', singleton('File')->dbObject('Kategori')->enumValues()));
$fields->push(new SimpleTreeDropdownField('SiteLinkID','Vælge en side (hvis kategorien er et link)'));
$fields->push(new FileIFrameField('BilledeThumb'));
}
return $fields;
}
Would you consider this good practise or is there a smarter way?