Trying to set an event using trigger

Hi

We have a 19c database in which we are trying to set an event using after startup trigger

create or replace trigger db_startup_trigger

 after startup on database

begin

 execute immediate 'alter system set events = '28500 trace name context forever, level 2 ';'

end;

/ 

But it is compiling with error

Warning: Trigger created with compilation errors.

SQL> show err

Errors for TRIGGER DB_STARTUP_TRIGGER:

LINE/COL ERROR

-------- -----------------------------------------------------------------

2/49   PLS-00103: Encountered the symbol "28500" when expecting one of

     the following:

     * & = - + ; < / > at in is mod remainder not rem return

     returning <an exponent (**)> <> or != or ~= >= <= <> and or

     like like2 like4 likec between into using || multiset bulk