Help to create a dynamic table

[rac123]

Please look at the jpg in this screenshot. I want to create something in HTML. How should I do this?

Basically, it's a hierarchy of certain data and when the user clicks on the + sign next to a data row, it will add the children rows (calls server to grab new data, the logic to do server part is already implemented).

Only tricky part that I'm stuck, here is, how to align the columns 2 (Page Views) & 3 (Visitors) everytime I add new row in the table.

Any help (idea) to implement this will be appreciated. How can I use CSS to resolve the issue? Should I use TABLE or DIV and how?

Thx,
Rach