Parse number data w/ dots for treeview

I need to take the example data below and put it in a treeview control, but since there's no parent/child relationship and it's all in one column. I don't know how to approach this.

Our table as it sits right now, has the column (which is a primary key / nvarchar(100)) in question looking like:

D1
D1.01
D1.01.01
D1.01.01.02
D1.01.01.02.003
D1.01.02
D1.01.02.02
D1.01.02.03
E1
E1.01
E1.01.01
E1.01.01.02.003
E1.01.02
E1.01.02.02
E1.01.02.033
E1.01.02.04

So, I'm thinking I have to look for the first "dot" and pull out the characters before that for the first nodes:
D1
E1

....then look for the 2nd "dot" and pull every thing before that for the second drill down node if the user were to click on either "D1" or the "E1" nodes..and they'd see:
D1
D1.01
E1
E1.01

I think there's a strip or some function to do that, but I'm a bit stumped right now. I've seen some stuff on hierarchical data, but I'm not gettin' it.

Any suggestions are welcome!

Thanks!