Hello kyveri,

At that moment we have not such kind functionlity (to represent milestone) in our GanttChart, but you could achieve this behavior if you are using FillSceneGraph event and implement the code below:

private void ultraChart1_FillSceneGraph(object sender, Infragistics.UltraChart.Shared.Events.FillSceneGraphEventArgs e)
        {
            List<Primitive> listPr = new List<Primitive>();
            foreach (Primitive pr in e.SceneGraph)
            {
                if (pr.GetType() == typeof(Box) && pr.Column != -1 && pr.Row != -1)
                {
                    int k = ((Box)pr).rect.Width;
                    DateTime[] dt = ((Box)pr).Value as DateTime[];
                    if (dt != null && dt[0] == dt[1])
                    {
                        Box mm = new Box(new Rectangle(((Box)pr).rect.X - (((Box)pr).rect.Height / 2), ((Box)pr).rect.Y, ((Box)pr).rect.Height, ((Box)pr).rect.Height));
                        mm.PE.Fill = Color.Red;
                        mm.RotationAngle = 45;
                        listPr.Add(mm);
                    }
                }
            }
            foreach (Primitive item in listPr) e.SceneGraph.Add(item);
        }

Please take a look at the attached sample and video file for more detaila and let me know if you have any questions