Code

float FitChildren(DiagramNode root, float minWidth, float padding)
{
	float total = 0;
	foreach (DiagramNode child in root.Query("outlinks/destination"))
		total += FitChildren(child, minWidth, padding) + padding;
	total = Math.Max(total - padding, minWidth);

	RectangleF r = root.Bounds;
	r.Width = total;
	root.Bounds = r;

	return total;
}

void Arrange(DiagramNode root, float levelHeight, float padding)
{
	float x = root.Bounds.Left;
	foreach (DiagramNode child in root.Query("outlinks/destination"))
	{
		child.Move(x, root.Bounds.Top + levelHeight);
		x = child.Bounds.Right + padding;
		Arrange(child, levelHeight, padding);
		StraightenLink(child.IncomingLinks[0]);
	}
}

void StraightenLink(DiagramLink link)
{
	RectangleF r = link.Destination.Bounds;
	float x = r.Left + r.Width / 2;
	link.Style = LinkStyle.Polyline;
	link.SegmentCount = 1;
	link.ControlPoints[0] = new PointF(x, link.ControlPoints[0].Y);
	link.ControlPoints[1] = new PointF(x, link.ControlPoints[1].Y);
}

private void btnTestLayout_Click(object sender, EventArgs e)
{
	DiagramNode root = diagram.ActiveItem as DiagramNode;
	if (root != null)
	{
		FitChildren(root, 32, 8);
		Arrange(root, 32, 8);
	}
}