SQL> CREATE TABLE trigger_test (id INT NOT NULL)
  2  /

Table created

Executed in 0,031 seconds
SQL> INSERT
  2  INTO   trigger_test
  3  SELECT level
  4  FROM   dual
  5  CONNECT BY
  6     level <= 1000000
  7  /

1000000 rows inserted

Executed in 1,469 seconds
SQL> COMMIT
  2  /

Commit complete

Executed in 0 seconds
SQL> TRUNCATE TABLE trigger_test
  2  /

Table truncated

Executed in 3 seconds
SQL> CREATE TRIGGER trg_test_ai
  2  AFTER INSERT
  3  ON trigger_test
  4  FOR EACH ROW
  5  BEGIN
  6     NULL;
  7  END;
  8  /

Trigger created

Executed in 0,094 seconds
SQL> INSERT
  2  INTO   trigger_test
  3  SELECT level
  4  FROM   dual
  5  CONNECT BY
  6     level <= 1000000
  7  /

1000000 rows inserted

Executed in 17,578 seconds