Dividing values from a single column into 2 based on a rule
Use a CASE statement in the column list to check if ParentID is 1 or null.

SQL Fiddle

PostgreSQL 9.3 Schema Setup:

create table YourTable
(
    Name varchar(10),
    ItemID int,
    ParentID int
 );

 insert into YourTable(Name, ItemID, ParentID) values('A', 1, null);
 insert into YourTable(Name, ItemID, ParentID) values('B', 2, null);
 insert into YourTable(Name, ItemID, ParentID) values('C', 3, null);
 insert into YourTable(Name, ItemID, ParentID) values('D', 4, null);
 insert into YourTable(Name, ItemID, ParentID) values('A1', 5, 1);
 insert into YourTable(Name, ItemID, ParentID) values('A2', 6, 1);
 insert into YourTable(Name, ItemID, ParentID) values('A3', 7, 1);
 insert into YourTable(Name, ItemID, ParentID) values('B1', 8, 2);
 insert into YourTable(Name, ItemID, ParentID) values('B2', 9, 2);
 insert into YourTable(Name, ItemID, ParentID) values('B3', 10, 2);


Query 1:

select case when ParentID is null then T.Name end as Column1,
       case when ParentID = 1 then T.Name end as Column2
from YourTable as T;


Results:

| column1 | column2 |
|---------|---------|
|       A |  (null) |
|       B |  (null) |
|       C |  (null) |
|       D |  (null) |
|  (null) |      A1 |
|  (null) |      A2 |
|  (null) |      A3 |
|  (null) |  (null) |
|  (null) |  (null) |
|  (null) |  (null) |