Applying css class to a row in a tree

Hi,



I am using an 'Ext.tree.Panel' and I would like to apply a css class to the first level of expandable items (I have rootVisible set to false) but I can't see how to do this. Does anyone know a good way to do this - i.e. what to extend or a value to add to the TreeStore? I did look at creating my own columns but this will only be applied to the single cell (and I would need to do for each column type).



Thanks in advance,

Paul