Hi, 

Option 1:  Add an additional column in RD and add aggregate count, the system shows result in tree view but additional column is added.

Option 2: Create database view and format the data, connect the view with report definition. Demo for sample data

create table dept(   
  username     varchar2(14),   
  workbasket      varchar2(14)   
);

insert into dept (username,workbasket) values ('abc','Manager');
insert into dept (username,workbasket) values ('abc','admin');
insert into dept (username,workbasket) values ('xyz','Developer');
insert into dept (username,workbasket) values ('xyz','Manager');
insert into dept (username,workbasket) values ('xyz','tester');
insert into dept (username,workbasket) values ('admin','Manager');

select * from dept;

---query to format the data 

WITH rpt 
     AS (SELECT c.*, 
                rownum rn 
         FROM   (SELECT username, 
                        workbasket 
                 FROM   dept 
                 ORDER  BY 1, 
                           2) c) 
SELECT CASE 
         WHEN a.username = b.username THEN ' ' 
         ELSE a.username 
       END username, 
       a.workbasket 
FROM   rpt a 
       LEFT OUTER JOIN rpt b 
                    ON a.rn = b.rn + 1 
ORDER  BY a.rn; 

---create view 

Create view demoBreakOn AS 
WITH rpt 
     AS (SELECT c.*, 
                rownum rn 
         FROM   (SELECT username, 
                        workbasket 
                 FROM   dept 
                 ORDER  BY 1, 
                           2) c) 
SELECT CASE 
         WHEN a.username = b.username THEN ' ' 
         ELSE a.username 
       END username, 
       a.workbasket 
FROM   rpt a 
       LEFT OUTER JOIN rpt b 
                    ON a.rn = b.rn + 1 
ORDER  BY a.rn; 


-- table result

select * from dept;

---view result

select * from demoBreakOn;