postgresql hierarchy table based on two column

I need to make sure we have support to create a hierarchy table based on a "father/son" table. Example:

Expected result:

Any idea, suggestion?

Thank you

with 
recursive cte(id, path) as
(
select f, f::text from   t where  f not in(select s from t where s is not null)
union all
select t.s, cte.path || '/' || t.s from cte join t on cte.id = t.f 
)

select  id      
       ,path[1] as root
       ,path[2] as l1
       ,path[3] as l2
       ,path[4] as l3
       ,path[5] as l4
from 
(
select  id 
       ,regexp_split_to_array(path, '/') as path
from    cte
) cte

Fiddle