This worked perfectly.
Just to further clarify for those interested it the addition of a second data set that stacks the values:
series1Data = new ObservableCollection<ChartDataPoint>();
series2Data = new ObservableCollection<ChartDataPoint>();
series1Data.Add(new ChartDataPoint("John", 25));
series2Data.Add(new ChartDataPoint("John", 45));
will create a stacked bar for John