<Style TargetType="{x:Type TreeViewItem}" x:Key="ItemStyleProject">
            <Setter Property="Foreground" Value="{StaticResource ResourceKey= BlackBrush}"/>
            <Setter Property="BorderBrush" Value="{StaticResource ResourceKey= RedBrush}"/>
            <Setter Property="BorderThickness" Value="3"/>
            <Setter Property="HorizontalContentAlignment" Value="Center"/>
            <Setter Property="Margin" Value="8"/>
            <Setter Property="Padding" Value="50,8,50,8"/>
            <Style.Triggers>
                <Trigger Property="IsSelected" Value="True">
                    <Setter Property="Control.Background" Value="Red"/>
                </Trigger>
            </Style.Triggers>
        </Style>

 <TreeViewItem Header="Item" Style="{StaticResource ResourceKey=ItemStyleProject}"