Merge inserted and deleted tables in SQL trigger

I have a table with a Balance column of type decimal(18,0).

I want to get updates to its Balance field and reflect the changes in the parents of the updated row.

Currently I can easily subtract parent values by selecting from deleted table and add to parent values by selecting from inserted table in two different queries. Since the updates will trigger an other update and so the concept of recursive triggers (enabled in my database) comes to scene, I want to have the minimum number of updates.

Is the following the best way to merge inserted and deleted table and to get the real difference in Balance field?

Update MyTable
Set Balance += updated.Price
From (  
    Select  IsNull(inserted.ParentID, deleted.ParentID) As ParentID, 
            (IsNUll(inserted.Balance,0) - IsNull(deleted.Balance,0))  As Price 
            From inserted
            Full join deleted
            on inserted.ID = deleted.iD
            WHERE IsNull(inserted.ParentID, deleted.ParentID) IS NOT NULL
) As updated
INNER JOIN MyTable
ON MyTable.ID = updated.ParentID
Where updated.ParentID IS NOT NULL

For example changing Balance from 1000 to 800 should yield to -200 change in parent Balance fields.

Also, my code fires the trigger one extra time, so that for an update in level 3 I get 4 updates (trigger-firing) instead of 3.