I needed to use the OnGetNodeInfo callback of a Zen <dynaTree>, because this seems to be the only way to control the style separately for different levels of the tree. This post describes two discoveries I made.
How a dynaTree builds a tree via the OnGetNodeInfo callback
When you use a dynaTree with the OnGetNodeInfo callback, the dynaTree creates a series of nodes and displays them top to bottom in the order they were created.