Find the entire tree from the root giving any node

Question

How do I find the entire tree given a node of a tree?

Example of tree:

       100
  101        102
1010 1011   1020  1021


select level, employee_id         


        

Answer 1

Why not just:

select level, employee_id, last_name, manager_id ,
connect_by_root manager_id as root_id
from employees
connect by prior employee_id = manager_id
start with manager_id = 100

Here is a fiddle

EDIT
Here is another try (After understanding the full problem):

with t as (
select case when mgr.employee_id is null then
1 else 0 end is_root, emp.employee_id employee, emp.manager_id manager, emp.last_name last_name

from employees mgr right outer join employees emp
on mgr.employee_id = emp.manager_id
),
tmp as (

select level, employee, last_name, manager ,
connect_by_root manager as root_id,
manager||sys_connect_by_path(employee,
',') cbp

from t
connect by prior employee = manager
start with t.is_root =
1 )
select * from tmp
where tmp.root_id in (select root_id from tmp where employee= 101 or manager = 101)

I checked it with 100, 101 and 1010 and it worked well
Here is a fiddle