Hi,
You could set the node's Shape to the one below, and set node.Stroke = Brushes.Transparent when only the top and right borders should be left visible. Set the decoration line colors to the ones you use for the nodes.
Shape topRightBorders = new Shape(
Shapes.Rectangle.Outline,
new[]
{
new LineTemplate(0, 0, 100, 0, Colors.Black, DashStyles.Solid, 1),
new LineTemplate(100, 0, 100, 100, Colors.Black, DashStyles.Solid, 1)
},
null, FillRule.Nonzero, "TopRightBorders");
Alternatively, use custom drawing to draw lines from the DrawNode event handler.
I hope that helps,
Stoyan