insert Document form fileTree

I have a Field with inputType: fileTree and want it to insert into an url. With this code it returns +9 instead of the documentUrl. How can I input documentsUrl via fileTree?

$this->Template->id = $this->id;
$this->Template->headline = $this->headline;
$this->Template->shorttext = $this->shorttext;
if($this->url)
$this->Template->url = $this->url;
else
$this->Template->url = $this->document;

$GLOBALS['TL_DCA']['tl_content']['fields']['document'] = array
(
'label' => &$GLOBALS['TL_LANG']['tl_content']['document'],
'inputType' => 'fileTree',
'eval' => array('files'=>true,'mandatory'=>false, 'fieldType'=>'radio')
);
$GLOBALS['TL_DCA']['tl_content']['fields']['url']['eval']= array('mandatory'=>false);