SQL & PL/SQL :: Error For Creating Tree Structure - Not Showing All Records

I have one table test_pc :

EVENT_IDPARENT_EVENT_ID
2001
2002 2001
1001 2002
1002 1001
1004
1003 2005
1006

Scripts are mentioned below :

create table test_pc
(event_id number(10), parent_event_id number(10));
insert into test_pc values(2001,null);
insert into test_pc values(1006,null);
insert into test_pc values(1004,null);
insert into test_pc values(2002,2001);
insert into test_pc values(1001,2002);
insert into test_pc values(1002,1001);
insert into test_pc values(1003,2005);

In order to derive parent child relationship I have ran the following query :

select *
from test_pc
start with parent_event_id is null
connect by nocycle prior event_id = parent_event_id;

It is giving all the records except the last one (i.e. event_id = 1003 and parent_event_id = 2005), because the parent_event_id does not exists in the table.

But my requirement is to show all the record, i.e. if the parent_child relationship is present then show accordingly and also show the rest of the records where the parent_child does not exists even the parent_event_id exists.