SELECT vo_group_id,
vg.name,
vg.vehicle_owner_id,
vg.graphical_symbol,
vg.lm_comment,
vg.company_nr,
vg.parent_vo_group_id,
(SELECT COUNT(*) FROM vo_group vgg CONNECT BY prior vg.vo_group_id = vg.parent_vo_group_id START WITH vgg.parent_vo_group_id =vg.vo_group_id) "Children_count"
FROM vo_group vg
CONNECT BY prior vg.vo_group_id = vg.parent_vo_group_id
START WITH vg.parent_vo_group_id IS NULL
ORDER siblings BY vg.parent_vo_group_id, vg.vo_group_id;