How to change string output in hierarchy tree postgresql?

I have a table like this:

------------------------------------------------- |  id  | description         | parent_id   |  cost -------------------------------------------------- | 1    |  Radiology         |       NULL  | 0.00 | 2    |  Lab Tests         |       NULL  | 0.00 | 3    |  Normal Radiology  |         1   | 0.00 | 4    |  Resonance         |         1   | 100.00 | 1100 |  Cerebral Resonance|         4   | 200.00 | 1900 |  Blood Tests       |         2   | 10.00 | 2044 |  Calcium           |         2   | 50.00  --------------------------------------------------- 

I need to generate this kind of output:

Radiology    -->Normal Radiology    -->Resonance       -->Cerebral Resonance with contrast Lab Test     --> Blood Test     --> Calcium 

I’m working on Postgresql. I’ve been trying this with recursive CTE but I was unable to generate what I like:

WITH RECURSIVE hierarchy AS (     SELECT  id, CAST(description AS TEXT) AS parent_list     FROM    orders     WHERE   parent_id is null     UNION       SELECT  c.id,             CAST(c2.parent_list || ' --> ' || c.description as text) as parent_list     FROM orders c     INNER JOIN hierarchy c2 ON c.parent_id = c2.id )    SELECT  id, parent_list FROM    hierarchy GROUP BY id, parent_list ORDER BY parent_list; 

That recursive CTE produces the following non desirable output:

Radiology Radiology--> Normal Radiology Radiology--> Resonance Radiology--> Resonance --> Cerebral Resonance with contrast Lab Test Lab Test --> Blood Test Lab Test --> Calcium 

Can anyone please give a piece of advice?