Transaction count having more than one Department

Dear Experts,

I am facing problem in creating a variable to calculate all those transaction having more than one department

We have department like Perfume, cosmetic, watches.

For example a customer comes to our shop and purchase from two department

1 watch

1 Perfume

So here transaction count is 1 but Department count is 2.

Because he purchase item from two different department.

I want to find all those transaction having more than one Department.

Please help me.

Thanks