recursive loop for creating cumulative sum

I want to build the following loop :

input: 1. monthly sales values columns (sales 01-2018, sales 02-2018, …, sales 12-2024) 2. conract value

output: these monthly columns: “contract value - sales 01-2018”, “contract value - (sales 01-2018+sales 02-2018)”, “contract value - (sales 01-2018+sales 02-2018+sales 03-2018)”, …, “contract value - (sales 01-2018+sales 02-2018+ … +sales 12-2024)”

I have already created the monthly sales columns using a loop, but since I need a cumulative sum of the previous iterations of this loop, I guess it is not possible to add an expression to my previous node. Now I am trying to use a recursive loop to get the cumulative sum of the previously created sales reports. Any suggestion on how I should proceed?