To reproduce:
- Bind to object-relational data
- Add node via the context menu.
- The DataBoundItem in the NodeAdding and NodeAdded events is null.

Workaround:
- Add the node in the code behind:
private void RadTreeView1_NodeAdding(object sender, RadTreeViewCancelEventArgs e)
{
    e.Cancel = true;
    RadTreeNode node = radTreeView1.SelectedNode;
    if (node.Level == 0)
    {
        data.Add(new MyParentClass() { Text = "test" });
    }

}