hierarchical query

Hi,Can someone help explain why is this.

SELECT last_name
  FROM employees
 WHERE department_id = 110

LAST_NAME
-----------
Higgins 
Gietz   

SELECT last_name
  FROM employees
 WHERE department_id = 110
CONNECT BY PRIOR employee_id = manager_id

LAST_NAME
----------
Higgins 
Gietz   
Higgins 
Gietz   
Gietz   
Higgins 
Gietz   

Why am I getting duplicate rows?

Thanks in advance,
Sha