Sample Data:
CREATE TABLE table_name ( value VARCHAR2(50) );
INSERT INTO table_name ( value ) VALUES ( 'A,B,C,D,E' );
Query:
WITH items ( list, item, lvl ) AS (
SELECT value,
REGEXP_SUBSTR( value, '[^,]+', 1, 1 ),
1
FROM table_name
UNION ALL
SELECT value,
...
