PL/pgSQL user-defined-function for update a list of data

Question

I am written a user-defined-function using PL/pgSQL given below:

CREATE OR REPLACE FUNCTION update_balance(id_input varchar, amount_input dec)
RETURNS TABLE (d_id varchar, d_parent_id varchar, d_balance dec) AS $$
DECLARE
    d_id varchar;
    d_parent_id varchar;
    d_balance dec;
BEGIN
    SELECT gl.id, gl.parent_id, gl.balance
    INTO d_id, d_parent_id, d_balance
    FROM gl
    WHERE gl.id = id_input;
    
    UPDATE gl
    SET balance = d_balance + amount_input
    WHERE gl.id = id_input;
    
    WHILE d_parent_id IS NOT NULL LOOP      
        SELECT gl.id, gl.parent_id, gl.balance
        INTO d_id, d_parent_id, d_balance
        FROM gl
        WHERE gl.id = d_parent_id;
        
        UPDATE gl
        SET balance = d_balance + amount_input
        WHERE gl.id = d_parent_id;

        d_balance := 0;
    END LOOP;
END
$$ LANGUAGE plpgsql;

And my data set looks like below:

{'id':1,'parent_id':NULL,'balance':0.0}
{'id':4,'parent_id':1,'balance':0.0}
{'id':14,'parent_id':4,'balance':0.0}
{'id':25,'parent_id':14,'balance':0.0}
{'id':120,'parent_id':25,'balance':0.0}

After this, I called the function below:

SELECT update_balance('120', 100.0);

After this, the result looks like below:

{'id':1,'parent_id':NULL,'balance':300.0}
{'id':4,'parent_id':1,'balance':200.0}
{'id':14,'parent_id':4,'balance':100.0}
{'id':25,'parent_id':14,'balance':0.0}
{'id':120,'parent_id':25,'balance':100.0}

ID 25 updated, which is fine, ID 14 didn't update, which is not fine, ID 4 updated, which is fine, ID 1 updated twice, which is not fine.

I don't understand why this is happening. I need to know why this is happening and to prevent this.

My expected result is, after calling the function update_balance() ID 120, 25, 14, 4, 1's balance will be plus 100 with it's current balance.

As I noticed I called the function to sum value 100 with current balance, but it's sum value multiplying every time once.