Derived Column based on Previous Value in Same

Dear Experts,

I have apparantly simple problem but finding it hard to resolve.

So, I got a table with 2 columns in Power BI as below.

Item ID----Session

A ----1

A ----2

B ----1

B ----4

B ----5

I need to find, how many Item arrived in a Session which was not in Previous Session. i.e.

Session ----New Item ----Comment
1 ----2 ----Both A & B
2 ----0 ----Nothing New, Since A was there on Session 1 already
3 ----0 ----Nothing
4 ----1 ----B - In this occasion B appeared in Session 4 but it was not there in Session 3
5 ----0 ----Nothing new, Since B was there on session 4 already

Now to achieve that basically what I am looking for is a "Derived Column" as below...

Is this possible that way please? 

Another alternate hack someone suggested me is create another derived table etc. but if the above (Derived Column) idea is feasible then I dont want to go that way.