sql - Repeated rows in 'connect by prior' clause in oracle -

i trying understand 'connect prior' clause in oracle. have created below table : create table emp_mgr ( mgr varchar2(10), emp varchar2(10) )

below data of table

mgr   emp null   f f      f      b f      c b      x b      y

now, when run below query

select mgr,emp emp_mgr connect prior emp = mgr start mgr null

below output of above query:

mgr     emp null     f f        f        b b        x b        y f        c

i understand output completely. problem when execute same query without 'start with' clause getting below output :

mgr     emp f       f       b b       x b       y f       c b       x b       y null    f f       f       b b       x b       y f       c

please explain why output repeated. why getting rows when not using start clause

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