Bagaimana cara mendapatkan jumlah anak total untuk semua orang tua dalam hierarki pohon Oracle?

Saya berpikir seperti ini:

select link, count(*)-1 as "RESULT COUNT"
  from (
    select connect_by_root(link_id) link
    from my_table
    connect by nocycle parent_link_id = prior link_id
    start with parent_link_id is null)
group by link
order by 1 asc