SQL & PL/SQL :: Convert ID And Comma Delimited List To Rows

how can I convert

select 1 as id, 'role1,role2,role3' as roles from dual union all
select 2 as id, 'role1' as roles from dual

to

select 1 as id, 'role1' as roles from dual union all
select 1 as id, 'role2' as roles from dual union all
select 1 as id, 'role3' as roles from dual union all
select 2 as id, 'role1' as roles from dual

?

I would prefer sql then plsql. Script for creating a test table:

create table CONVERT_LIST(id integer, roles varchar2(100));
insert into CONVERT_LIST values(1,'role1,role2,role3');
insert into CONVERT_LIST values(2,'role1');