Power BI dax function to add number from previous cell in same column

enter image description hereI have been doing some analysis based on customer orders in excel, now i want to replicate same in power BI. Having trouble in one "if formula"

In this formula i want to see purchase rate of customer based on how many time they come Excel formula is =if(A3=A2,B2+1,1)

In power BI i unable to add number from above cell. Please help me regarding this issue. I am new to Power BI.