How can I change string output in a hierarchy tree with 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 contrastLab Test    --> Blood Test    --> Calcium

I'm working on PostgreSQL. I've been trying this with a 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_listFROM     hierarchyGROUP BY id, parent_listORDER BY parent_list;

That recursive CTE produces the following nondesirable output:

RadiologyRadiology--> Normal RadiologyRadiology--> ResonanceRadiology--> Resonance --> Cerebral Resonance with contrastLab TestLab Test --> Blood TestLab Test --> Calcium

How can I do it?