Over my head

If you look in the current release of dojo you wont find a GridTree.

However, if you are willing to pull down the full dojo source code (including dojox and the utils etc) from the svn repository and apply the patch associated with ticket #7402, when you build the source, you'll find yourself the proud owner of an unsupported dojox.grid.TreeGrid.

It works well and if you look in the dojox grid tests directory you'll find the file test_tree_grid.html which is a good example of how to use it.