如何使用ItemSource将其他项添加到WPF ListBox？

<ListBox ItemsSource="{Binding MyDataList}">

public ObservableCollection<string> MyDataList { get; set; }

MyDataList = new ObservableCollection<string>();
MyDataList.Add("Item 1");
MyDataList.Add("Item 2");
MyDataList.Add("Item 3");

MyDataList.Add("Item 4");

public class MyViewModel : INotifyPropertyChanged
{
    public event PropertyChangedEventHandler PropertyChanged;

    protected void OnPropertyChanged(string propertyName)
    {
        PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
    }
}

MyDataList.Add("Item 4");
OnPropertyChanged("MyDataList");