<Window x:Class="Test.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:scm="clr-namespace:System.ComponentModel;assembly=WindowsBase"
        Title="MainWindow" Height="350" Width="525">
    <Window.Resources>
        <CollectionViewSource x:Key="Subjects" Source="{Binding Subjects}">
            <CollectionViewSource.SortDescriptions>
                <scm:SortDescription PropertyName="IncludeKey" />
            </CollectionViewSource.SortDescriptions>
        </CollectionViewSource>
    </Window.Resources>