Go to http://revealnet.com/pipelines/plsql/archives.htm read 'Using Order By with Connect By' and get hierarchy package. Then do something like this...
Code:
Oracle8i Enterprise Edition Release 8.1.7.4.0 - Production
JServer Release 8.1.7.4.0 - Production

SQL> CREATE OR REPLACE PACKAGE hierarchy
  2  IS
  3    TYPE branchtabletype IS TABLE OF VARCHAR2 (4000)
  4      INDEX BY BINARY_INTEGER;
  5  
  6    branchtable branchtabletype;
  7  
  8    FUNCTION branch (
  9      vlevel IN NUMBER,
 10      vvalue IN VARCHAR2,
 11      vdelimiter IN VARCHAR2 DEFAULT CHR (0))
 12      RETURN VARCHAR2;
 13  
 14  END hierarchy;
 15  /

Package created.

SQL> 
SQL> CREATE OR REPLACE PACKAGE BODY hierarchy
  2  IS
  3    returnvalue VARCHAR2 (4000);
  4  
  5    FUNCTION branch (
  6      vlevel IN NUMBER,
  7      vvalue IN VARCHAR2,
  8      vdelimiter IN VARCHAR2 DEFAULT CHR (0))
  9      RETURN VARCHAR2
 10    IS
 11    BEGIN
 12      branchtable (vlevel) := vvalue;
 13      returnvalue := vvalue;
 14  
 15      FOR i IN REVERSE 1 .. vlevel - 1 LOOP
 16        returnvalue := branchtable (i) || vdelimiter || returnvalue;
 17      END LOOP;
 18  
 19      RETURN returnvalue;
 20    END branch;
 21    
 22  END hierarchy;
 23  /

Package body created.

SQL> SELECT path 
  2  FROM  (SELECT path, LEAD (path) OVER ( 
  3                  ORDER BY ROWNUM) next_path 
  4         FROM  (SELECT ROWNUM row_num, 
  5                       hierarchy.branch ( 
  6                         LEVEL, ename, ', ') path 
  7                FROM   emp 
  8                START WITH mgr IS NULL 
  9                CONNECT BY PRIOR empno = mgr)) 
 10  WHERE  next_path NOT LIKE path || '%';

PATH
--------------------------------------------------------------------------------
KING, JONES, SCOTT, ADAMS
KING, JONES, FORD, SMITH
KING, BLAKE, ALLEN
KING, BLAKE, WARD
KING, BLAKE, MARTIN
KING, BLAKE, TURNER
KING, BLAKE, JAMES

7 rows selected.

SQL>