TreeViewItem Items Presenter has Height equal to the parent tree view - wpf

Question

I've got a custom style with a template for tree view items. I want the items presenter to display content in the width and height of the grid row that it is in and leave scrolling up to the child control. This works... sort of. The child does do the scrolling, but the height is for some reason set to the parent's height (tree view) this messes up the scrolling. I've copied the code below.
<Style TargetType="TreeViewItem">
<Setter Property="Background" Value="Transparent"/>
<Setter Property="Margin" Value="0"/>
<Setter Property="Padding" Value="0"/>
<Setter Property="VerticalContentAlignment" Value="{Binding Path=VerticalContentAlignment, RelativeSource={RelativeSource AncestorType={x:Type ItemsControl}}}"/>
<Setter Property="Padding" Value="1,0,0,0"/>
<Setter Property="HorizontalContentAlignment" Value="Center"/>
<Setter Property="Foreground" Value="{DynamicResource {x:Static SystemColors.ControlTextBrushKey}}"/>
<Setter Property="FocusVisualStyle" Value="{StaticResource TreeViewItemFocusVisual}"/>
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="TreeViewItem">
<Grid>
<Grid.RowDefinitions>
<RowDefinition Height="40"/>
<RowDefinition Height="*"/>
</Grid.RowDefinitions>
<Border Name="Bd" Background="LightGray" BorderBrush="Black" Grid.Row="0"
BorderThickness="1" Padding="{TemplateBinding Padding}">
<Grid Margin="5,0,5,0">
<Grid.ColumnDefinitions>
<ColumnDefinition Width="Auto"/>
<ColumnDefinition Width="*"/>
</Grid.ColumnDefinitions>
<Path x:Name="ExpandPath" HorizontalAlignment="Left" VerticalAlignment="Center" Margin="1,1,1,1"
Fill="{StaticResource GlyphBrush}" Data="M 0 4 L 16 4 L 8 12 Z" Grid.Column="0"/>
<Label Grid.Column="1" x:Name="PART_Header" Content="{TemplateBinding Header}" FontSize="18" FontWeight="Bold"
HorizontalAlignment="{TemplateBinding HorizontalContentAlignment}"/>
</Grid>
</Border>
<ItemsPresenter Name="ItemsHost" Grid.Row="1"/>
</Grid>
<ControlTemplate.Triggers>
<Trigger Property="IsExpanded" Value="false">
<Setter TargetName="ItemsHost" Property="Visibility" Value="Collapsed"/>
<Setter Property="Data" TargetName="ExpandPath" Value="M 8 0 L 16 8 L 8 16 Z"/>
</Trigger>
<Trigger Property="HasItems" Value="false">
<Setter TargetName="ExpandPath" Property="Visibility" Value="Collapsed"/>
</Trigger>
<MultiTrigger>
<MultiTrigger.Conditions>
<Condition Property="HasHeader" Value="false"/>
<Condition Property="Width" Value="Auto"/>
</MultiTrigger.Conditions>
<Setter TargetName="PART_Header" Property="MinWidth" Value="75"/>
</MultiTrigger>
<MultiTrigger>
<MultiTrigger.Conditions>
<Condition Property="HasHeader" Value="false"/>
<Condition Property="Height" Value="Auto"/>
</MultiTrigger.Conditions>
<Setter TargetName="PART_Header" Property="MinHeight" Value="19"/>
</MultiTrigger>
<Trigger Property="IsSelected" Value="true">
<Setter Property="IsExpanded" Value="True"/>
</Trigger>
<Trigger Property="IsSelected" Value="False">
<Setter Property="IsExpanded" Value="False"/>
</Trigger>
<Trigger Property="IsEnabled" Value="false">
<Setter Property="Foreground" Value="{DynamicResource {x:Static SystemColors.GrayTextBrushKey}}"/>
</Trigger>
</ControlTemplate.Triggers>
</ControlTemplate>
</Setter.Value>
</Setter>
<Style.Resources>
<Style TargetType="{x:Type TreeViewItem}">
</Style>
</Style.Resources>
</Style>

Answer 1

I figured out a way to do this in C# by setting the width and height of the child element when the selection changed.