Old pseudo record in After Insert Trigger

I've got the following test trigger which I copied from a book:

TRIGGER bef_ins_ceo_comp
   BEFORE INSERT
   ON ceo_compensation
   FOR EACH ROW
    DECLARE
   PRAGMA AUTONOMOUS_TRANSACTION;
BEGIN
   INSERT INTO ceo_comp_history
        VALUES (:NEW.name,
                :OLD.compensation, :NEW.compensation,
                'AFTER INSERT', SYSDATE);
   COMMIT;
END;

As you can see when inserting a new record to the ceo_comp_history t开发者_开发技巧able :OLD.compensation value is used. I wonder where does that :OLD pseudo record come from? It's not an update trigger to keep both :NEW and :OLD values.

My guess is the :OLD values will be all NULL. Code is probably just a copy/paste from the update trigger