First thing you should set chart properties.
Step 1: Go to Chart properties then click on Series.

Step 2 : Change the name of Series. Here, I set the name to Case. We can also change the ChartType

Change your code as follows :
chart1.DataSource = ds;
//set the member of the chart data source used to data bind to the X-values of the series
chart1.Series["Case"].XValueMember = Convert.ToString(x);
//set the member columns of the chart data source used to data bind to the X-values of the series
chart1.Series["Case"].YValueMembers = Convert.ToString(y);
chart1.Titles.Add("Case");