Depending on the platform, there are different SQL operators available to handle recursive parent/child connections for nested PK/FK relationships in a single table. Oracle uses a CONNECT BY clause while Postgres offers a WITH RECURSIVE/UNION ALL clause. Note the below Postgres query uses a CTE (common table expression) to add the Level column using AS. Once the Level column is established further queries allow creating a path of every tree vs. jus the results below that show where the children exist in the tree.

-- Create the Organization table
CREATE TABLE Organization (
    ID SERIAL PRIMARY KEY,
    ParentID INTEGER,
    Name TEXT
);

-- Insert sample data
INSERT INTO Organization (ParentID, Name) VALUES 
    (NULL, 'CEO'),
    (1, 'Manager1'),
    (1, 'Manager2'),
    (2, 'Employee1'),
    (2, 'Employee2'),
    (3, 'Employee3'),
    (3, 'Employee4');

WITH RECURSIVE HierarchyCTE AS (
    SELECT 
        ID,
        ParentID,
        Name,
        0 AS Level
    FROM 
        Organization
    WHERE 
        ParentID IS NULL
    
    UNION ALL
----------
    SELECT 
        t.ID,
        t.ParentID,
        t.Name,
        h.Level + 1
    FROM 
        Organization t
    JOIN 
        HierarchyCTE h ON t.ParentID = h.ID
)
---------
SELECT 
    ID,
    ParentID,
    Name,
    Level
FROM 
    HierarchyCTE
ORDER BY 
    Level, ID;