How to make AppSettings work with multiple values for a key

using System.Configuration;
using System.Text;
using System.Windows.Forms;

namespace ConfigurationTest
{
	public class App
	{
		static void Main()
		{
			StringBuilder sbConcatenated = new StringBuilder();
			StringBuilder sbIndividual = new StringBuilder();
			foreach(string key in ConfigurationSettings.AppSettings)
			{
				sbConcatenated.Append(key + "=" + ConfigurationSettings.AppSettings[key] + "\n");
				sbIndividual.Append(key + "\n");
				foreach(string value in ConfigurationSettings.AppSettings.GetValues(key))
				{
					sbIndividual.Append("\t" + value + "\n");
				}
			}
			MessageBox.Show("CONCATENATED:\n" + sbConcatenated.ToString() +
				"\nINDIVIDUAL:\n" + sbIndividual.ToString(), "AppSettings");
		}
	}
}