SQL & PL/SQL :: CREATE OR REPLACE - Error During Execution Of Trigger

I create this trigger:

CREATE OR REPLACE TRIGGER T_HST AFTER INSERT
On HST
FOR EACH ROW
DECLARE
Begin
INSERT INTO HST (EMP_NO, START_DATE )
SELECT EMP_NO, SYSDATE
FROM HST
WHERE EMP_NO = :NEW.EMP_NO;
End T_HRS_SAL_PERIOD_HSTY_UPD_PRI;
/

when I insert a new record in table HST I get this error:

ORA-04091: table HST is mutating, trigger/function may not see it
ORA-06512: at "T_HST", line 3
ORA-04088: error during execution of trigger 'T_HST'

What I wrong in this trigger?How can I modify it?