Seems that you have a bug in your handler. If you want to select all subnodes try this:
private void machinesTreeView_SelectedNodeChanged(object sender, RadTreeViewEventArgs e)
{
for (int w = 0; w < machinesTreeView.SelectedNode.Nodes.Count; w++)
{
machinesTreeView.SelectedNode.Nodes[w].Selected = true;
}
}
Do not forget to enable multiselect feature:
machinesTreeView.MultiSelect = true;