I am trying to make a column plot with two groups of data.

A a1 2
a2 2.5

B b1 3
b2 5.5

I am trying to make a1, a2, b1, b2 as stand alone column and I also want to
have a series name for a1, a2 and another name for b1 and b2. Can I do this
in Excel?

If I try to make two series, it can only have 2 x axis values. Basically, I
want to plot series A first and then series B. But I want to put them in the
same plot.. Many Thanks.