How can we create an Item Discount Promotion with a quantity specification

Summary:

We need to create an Item Discount Promotion with a quantity specification, how can we do it?

Content (required):

Hello, we need some info on how to create an item discount promotion that is applied only with a specific quantity of items on cart. For example: The promotion is only applied after more than 20 items (for a SKU) in the cart, It will give 10% off on all those items for that SKU. 

How can we achieve that?

We would like to consult oracle before starting developing some solution, to find the best way to achieve that requirement.

Thank you!