SAP CDS hierarchy View

[JamesG]

Hi experts:

I want use parent field in hierarchy View,but I get this error :

This is my code :

define hierarchy ZDDl_PP003B
  with parameters
    P_MATNR : abap.char( 40 )
  as parent child hierarchy(
    source ZDDL_PP003A
    child to parent association _PARENT
    start where
          matnr = :P_MATNR
    siblings order by
      matnr
    multiple parents allowed  )
{
$node.hierarchy_level as levels,
  werks,
  stlan,
  stlal,
  matnr,
  bmeng,
  bmein,
  datuv,
  valid_to,
  idnrk,
  menge * _PARENT.bmeng as menge,
  meins,
  _PARENT

}

Best Regards