Code

TreeLayout tl = new TreeLayout();
tl.NodeDistance = 0;
tl.Arrange(diagram);

DiagramNodeCollection nodes = new DiagramNodeCollection();
GetBfsOrder(root, nodes);

for (int i = 1; i < nodes.Count; ++i)
{
	DiagramNode node = nodes[i];
	PointF p = node.Bounds.Location;
	p.Y *= 2;
	if (i % 2 != 0)
		p.Y += node.Bounds.Height;
	node.Move(p.X, p.Y);
}

private void GetBfsOrder(DiagramNode root, DiagramNodeCollection nodes)
{
	Queue<DiagramNode> queue = new Queue<DiagramNode>();
	queue.Enqueue(root);

	while (queue.Count > 0)
	{
		DiagramNode node = queue.Dequeue();
		nodes.Add(node);

		foreach (DiagramLink link in node.OutgoingLinks)
		{
			DiagramNode child = link.Destination;
			if (!nodes.Contains(child) && !queue.Contains(child))
				queue.Enqueue(child);
		}
	}
}