Specific Product to be included on Quote's Total Discount

Hello. We have a 'Trade-In Discount' product that is added to quotes, where this negative amount is added to the product total.  This is a discount price and we want the 'Trade In' amount to show in our total discount. (So the customer understands the total amount they saved with their purchase)  Our total discount is (subtotal * discount ).

What formula is needed to include a specific product to our total discount?  I prefer the Product Hierarchy ID or Product ID #Formulas #Formula Field #Products #Quote Template #Quotes.    

Any assistance is appreciated.

mw