MSAGL Sub-graph 'Collapse' button not visible

Question

I am testing using Microsoft MSAGL to create a graph with Subgraphs. The API suggests there is a button to 'collapse' a sub-graph but the button is never visible. My Code is of the form

            var SubGraph = new MSAGL.Subgraph("Test");
            SubGraph.AddNode(Graph.FindNode("Node1"));
            SubGraph.AddNode(Graph.FindNode("Node2"));

            SubGraph.CollapseButtonColorActive = MSAGL.Color.Black;
            SubGraph.CollapseButtonColorInactive = MSAGL.Color.Red;

            SubGraph.Attr.FillColor = MSAGL.Color.AliceBlue;

            var SubGraph2 = new MSAGL.Subgraph("Test2")
            {
                DiameterOfOpenCollapseButton = 20,
                CollapseButtonColorActive = MSAGL.Color.Blue
            };

            SubGraph2.AddNode(Graph.FindNode("Node4"));
            SubGraph.AddSubgraph(SubGraph2);

            Graph.AddPrecalculatedEdge(new ReadsEdge(Node2, Node3));

            Graph.RootSubgraph.AddSubgraph(SubGraph);

Am I missing something?

Thanks