how to implement add using upsert and trigger?

Hi, all：
when I using upsert and trigger to update other table automatically：
create table stat_detail(itemid bigint not null, value bigint, captime bigint);
create table stat_result(itemid bigint primary key, value bigint, cnt bigint);

create or replace function inertfunc() returns trigger as $$
begin
insert into stat_result(itemid,value,cnt) values(new.itemid, new.value, 1)
on conflict(itemid) do update
set value = excluded.value + new.value, cnt = excluded.cnt +1 where excluded.itemid = new.itemid;
return new;
end;
$$
language plpgsql;

create trigger tri_insert after insert on stat_detail for each row execute function inertfunc();

postgres=# insert into stat_detail values(100,1,1);
INSERT 0 1
postgres=# select * from stat_result ;
itemid | value | cnt
--------+-------+-----
100 | 1 | 1
(1 row)

postgres=# insert into stat_detail values(100,1,1);
INSERT 0 1
postgres=# select * from stat_result ;
itemid | value | cnt
--------+-------+-----
100 | 2 | 2
(1 row)

postgres=# insert into stat_detail values(100,1,1);
INSERT 0 1
postgres=# select * from stat_result ;
itemid | value | cnt
--------+-------+-----
100 | 2 | 2
(1 row)

But I want it is "100 3 3". So how I can do?

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