SELECT Obs.OBS_ID,
       obs.NAME AS long_name,
       obs.parent_obs_id,
       obs.SHORT_NAME,
       obs.REF_NUMBER,
       obs.OBS_LEVEL,
       NVL2 (short_name, short_name || ' ' || name, name) AS Name
FROM obs obs
WHERE vehicle_owner_id = ?
AND ? IS NOT NULL
START WITH  obs.parent_obs_id IS NULL
CONNECT BY parent_obs_id = PRIOR obs.obs_id
ORDER SIBLINGS BY obs.SHORT_NAME, name,  obs.REF_NUMBER