How can I create a treemap using a directory structure?

Hello, I have a series of file paths (like d:\a\b\c), and I would like to create a treemap where the size of the box is proportional to the number of items that are in the directory.  Would anyone know how to do this?  My first thought would be to split the path by \ and then put each of the split strings in new columns, and use those columns for the treemap.  However, I can't figure out how to split the string and put it in a new column.  Is there a good way to do this?