Forms :: When Insert Detail The Data Insert Twice Time

when i tried to insert the details from oracle froms..the data inserts twice to the DB..

my table structure:

create table app_sri
(a_id integer primary key,
p_first_name varchar2(30),
p_last_name varchar2(20),
p_age number(3)
);

here a_id can be genarated through simple sequence(pid_seq)...
trigger on app_sri
create or replace trigger pid_trg

[Code]....

form insertion code..

Begin
insert into app_sri(null,'robo','Big',100);
commit
End;

the data inserted...but twice

what is the reason behind the double insertion?