1  declare
  2       cursor c is
  3            select level a,
  4                       case mod(level,2) when 0 then (
  5  select cast(collect(level) as sys.odcinumberlist)  from dual connect by level <= 3) end b
  6                  from dual
  7                  connect by level <= 6;
  8       type t is table of c%rowtype;
  9       v t;
 10  begin
 11       open c;
 12       fetch c bulk collect into v;
 13  /*
 14       forall i in 1..v.count
 15            insert into tmp$tab1(a)
 16                  values(v(i).a);
 17  */
 18       for i in 1..v.count loop
 19            if v(i).b is not null then
 20                  forall j in 1..v(i).b.count
 21                       insert into tmp$tab2(a, b)
 22                            values (v(i).a, v(i).b(j));
 23            end if;
 24       end loop;
 25* end;
SQL> /

PL/SQL procedure successfully completed.

SQL> select * from tmp$tab2;

         A          B
---------- ----------
         2          1
         2          2
         2          3
         4          1
         4          2
         4          3
         6          1
         6          2
         6          3

9 rows selected.