problem with RULE

I have two tables. One is test_main, and second is named result. Also I have
view which summarizes results from test_main table and groups them by ID
column:

************************
CREATE TABLE test_main(id varchar(4), value int4);

CREATE TABLE result(id varchar(4), value int4);

CREATE VIEW summing AS
SELECT test_main.id, sum(test_main.value) AS suma
GROUP BY test_main.id;
**************************

And here is my problem: I want to make a rule which will insert new row in
table result which will have ID and SUM value of that ID.
*************************
CREATE RULE tester AS
ON INSERT TO test_main

DO INSERT INTO "result" (id, value)
VALUES (new.id, summing.suma);
*************************
So, when this rule is executed, for this INSERT commands:
*************************
insert into test_main values('0003', 100)

insert into test_main values('0004', 100)
*************************
I get in column result:
*************************
0003, 100
0004, 100
0004, 100
**************************
and I need
*********************
0003, 100
0004, 100

Can anybody help me in doing this?
Thanks in advance