I have a treemap control that is pretty basic structure but displays strange blank area on top of the chart. 

I am using the following C# code. 

            _treemapView = new IGTreemapView ();

            _treemapView.Theme = new IGTreemapViewTheme3 ();
            _treemapView.Frame = new RectangleF (0, 100, 768, 600);
            _treemapViewDataSourceHelper = new IGTreemapViewDataSourceHelper (_data, _treemapView);
            _treemapViewDataSourceHelper.AddLevel ("Value", "Strategy", "Children");
            _treemapViewDataSourceHelper.AddLevel ("Value", "Fund", String.Empty);
            _treemapView.DataSource = _treemapViewDataSourceHelper;
            _treemapView.RootNode.Label = "Portfolio";
            this.View.Add (_treemapView);

The data class is:

    public class TreemapData : NSObject
    {
        [Export ("Value")]
        public float Value { get; set; }

        [Export ("Strategy")]
        public string Strategy { get; set; }

        [Export ("Fund")]
        public string Fund { get; set; }



        [Export ("Children")]
        public NSMutableArray Children { get; set; }
    }

Can someone suggest how to get rid of that too blank area.