Hyperlink in tree view

I want to add a hyperlink with ftp url in my tree view. i tested with adding widget="url" in my xml ,but its not working.
Please help
my code is
  <tree string="File Names" >
            <field name="time_created" string="Time Created"/>
            <field name="size" string="Size"/>
             <field name="file_name"/>
             <field name="file_path" widget="url"/>
   </tree>

class filedata(osv.osv):
    _name = 'filedata'
    _log_access = False
    _columns = {
        'file_name' : fields.char('Name'),
        'file_path' : fields.char('File Path'),
        'time_created' : fields.datetime('Date Time'),
        'size' : fields.char('Size')
    }