how to filter more than once in Microsoft.Win32.OpenFileDialog()

    Microsoft.Win32.OpenFileDialog dlg = new Microsoft.Win32.OpenFileDialog();
 dlg.FileName = "Document"; // Default file name
 dlg.DefaultExt = ".txt"; // Default file extension
 dlg.Filter = "Text documents (.txt)|*.txt"; // Filter files by extension here
 

I want to filter more than one type

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