<ToggleButton Height="24" ... IsChecked="{Binding IsCollapsed}">
    <ToggleButton.Template>
        <ControlTemplate TargetType="ToggleButton">
            <!-- тут пишете что угодно -->
            <DockPanel Background="Gray">
                <Border Background="Red" DockPanel.Dock="Left" Width="30"/>
                <Border Background="Yellow" DockPanel.Dock="Left" Width="30"/>
                <Border Background="Green" DockPanel.Dock="Left" Width="30"/>
                <Grid/>
            </DockPanel>
        </ControlTemplate>
    </ToggleButton.Template>
</ToggleButton>