drop table test21;
CREATE TABLE test21
AS SELECT * FROM emp
where 1<>2;

DECLARE

  CURSOR c1 IS SELECT * FROM emp;

TYPE t_emp IS TABLE OF c1%rowtype;

v_emp t_emp:=t_emp();

g_limit number:=1000;

BEGIN

OPEN c1;

  loop fetch c1  BULK COLLECT INTO  v_emp LIMIT g_limit;
  exit WHEN v_emp.count=0;
    forall i IN v_emp.FIRST..v_emp.LAST
	INSERT INTO test21
	  (empno,
	   JOB,    
	   ename,
	   hiredate,
	   deptno
	  )

    	VALUES
    	  (
    	   test21_seq.nextval,
	   v_emp(i).JOB,    
           v_emp(i).ename,
           v_emp(i).hiredate,
           v_emp(i).deptno
    );
  END loop;

COMMIT;
close c1;
end;

set serveroutput on
DECLARE 
  CURSOR c1 IS SELECT * FROM emp;
TYPE t_emp IS TABLE OF c1%rowtype;
v_emp t_emp:=t_emp();

g_limit number:=1000;
BEGIN
OPEN c1;
  loop fetch c1  BULK COLLECT INTO  v_emp LIMIT g_limit;
  exit WHEN v_emp.count=0;
  FOR i IN 1..v_emp.count
    loop
      IF v_emp(i).deptno=20 THEN
      --Create 1st record
      v_emp.EXTEND;
        v_emp(v_emp.LAST).deptno  :=v_emp(i).deptno;
        v_emp(v_emp.LAST).empno   :=v_emp(i).empno;
        v_emp(v_emp.LAST).ename   :='ab';
        v_emp(v_emp.LAST).JOB     :='ITCLERK';
        v_emp(v_emp.LAST).hiredate:='17-DEC-80';
      --Create 2nd record
      v_emp.EXTEND;
        v_emp(v_emp.LAST).deptno  :=v_emp(i).deptno;
        v_emp(v_emp.LAST).empno   :=v_emp(i).empno;
        v_emp(v_emp.LAST).ename   :='cd';
        v_emp(v_emp.LAST).JOB     :='xxx';
        v_emp(v_emp.LAST).hiredate:='17-NOV-80';
      END IF;
    end loop;
    forall i IN 1..v_emp.count
      INSERT INTO test21
      (empno,
       JOB,    
       ename,
       hiredate,
       deptno
       )
      VALUES
      (
      v_emp(i).empno,
      v_emp(i).JOB,    
      v_emp(i).ename,
      v_emp(i).hiredate,
      v_emp(i).deptno
      );
  END loop;
COMMIT;
close c1;
end;

Forget: you don't need to initialize the collection when you use it with BULK COLLECT, this later do it.

SQL> DECLARE
  2    CURSOR c1 IS SELECT * FROM emp;
  3  TYPE t_emp IS TABLE OF c1%rowtype;
  4  v_emp t_emp;
  5  g_limit number:=1000;
  6  BEGIN
  7  OPEN c1;
  8    loop fetch c1  BULK COLLECT INTO  v_emp LIMIT g_limit;
  9    exit WHEN v_emp.count=0;
 10    FOR i IN 1..v_emp.count
 11      loop
 12        IF v_emp(i).deptno=20 THEN
 13        --Create 1st record
 14        v_emp.EXTEND;
 15          v_emp(v_emp.LAST).deptno  :=v_emp(i).deptno;
 16          v_emp(v_emp.LAST).empno   :=v_emp(i).empno;
 17          v_emp(v_emp.LAST).ename   :='ab';
 18          v_emp(v_emp.LAST).JOB     :='ITCLERK';
 19          v_emp(v_emp.LAST).hiredate:='17-DEC-80';
 20        --Create 2nd record
 21        v_emp.EXTEND;
 22          v_emp(v_emp.LAST).deptno  :=v_emp(i).deptno;
 23          v_emp(v_emp.LAST).empno   :=v_emp(i).empno;
 24          v_emp(v_emp.LAST).ename   :='cd';
 25          v_emp(v_emp.LAST).JOB     :='xxx';
 26          v_emp(v_emp.LAST).hiredate:='17-NOV-80';
 27        END IF;
 28      end loop;
 29      forall i IN 1..v_emp.count
 30        INSERT INTO test21
 31        (empno,
 32         JOB,
 33         ename,
 34         hiredate,
 35         deptno
 36         )
 37        VALUES
 38        (
 39        v_emp(i).empno,
 40        v_emp(i).JOB,
 41        v_emp(i).ename,
 42        v_emp(i).hiredate,
 43        v_emp(i).deptno
 44        );
 45    END loop;
 46  close c1;
 47  end;
 48  /

PL/SQL procedure successfully completed.