How do I update a node in a TreeView when it has no parent?

[Edvin Syse]

Updating a node that has a parent, even changing it from a TreeNode to a 
BranchNode is trivial via det node.getParent().update() method. But when 
a node is at the root of the hierarchy, I don't have a parent to call 
update on. I guess I need to invoke some listener on the TreeView 
itselv, but how? :)

-- Edvin