Instead using:

insert into T1 (c1, c2)

select 1, 2;

insert into T1 (c1, c2)

select 3, 4;

or

insert into T1 (c1, c2)

select c1, c2

from (

select 1, 2;

union all

select 3, 4

) as Q(c1, c2)

use just one statement and the row constructor.

insert into T1(c1, c2) values (1, 2), (3, 4);

There is a limitation in the number of tuples (1000) that can be inserted using the row constructor.