Conditionally apply % discount to items based on number of unique items in cart (without an app)

[TothDigital]

We are a simple supplement store with only 4 products. I want to offer customers a "bundle" discount when they purchase multiple products, but I don't want to have to install and pay for yet another app. Hoping I can accomplish this with a simple conditional statement in the cart. Can someone please help me translate this to liquid? 😅

If cart has 2 unique SKUs, discount items 5% ;

If cart has 3 unique SKUs, discount items 10% ;

If cart has all 4 unique SKUs, discount items 15% ;

*The quantity of each unique SKU should not affect the discount. For instance, if cart has 1 of SKU-123 and 12 of SKU-456, the discount should still only be 5% 

Thanks for reading!