Hello,

Thank you for your post. I have been looking into it and I can suggest you use the following Style for the XamDataTree:

<Style xmlns:igDT="http://schemas.infragistics.com/xaml"
        xmlns:igPrimDT="http://schemas.infragistics.com/xaml/primitives"
        TargetType="igDT:XamDataTree">
    <Setter Property="Background" Value="White"/>
    <Setter Property="BorderThickness" Value="1"/>
    <Setter Property="Foreground" Value="Black"/>
    <Setter Property="Template">
        <Setter.Value>
            <ControlTemplate TargetType="igDT:XamDataTree">
                <Border x:Name="Bd" Background="{TemplateBinding Background}" BorderBrush="{TemplateBinding BorderBrush}" BorderThickness="{TemplateBinding BorderThickness}">
                    <Grid>
                        <Grid.RowDefinitions>
                            <RowDefinition Height="*"/>
                            <RowDefinition Height="Auto"/>
                        </Grid.RowDefinitions>
                        <Grid.ColumnDefinitions>
                            <ColumnDefinition Width="*"/>
                            <ColumnDefinition Width="Auto"/>
                        </Grid.ColumnDefinitions>
                        <igPrimDT:NodesPanel x:Name="NodesPanel" Background="Transparent" />
                    </Grid>
                </Border>
            </ControlTemplate>
        </Setter.Value>
    </Setter>

Please let me know if this helps you or you need further assistance on this matter.

Looking forward for your reply.