Treeviewitem togglebutton style working only for parent and not for child

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C#

WPF

I have a treeview, for which I wrote the style template of treeview in App.xaml, as I need to apply the style in two or three treeviews in my application. Now my problem is that the togglebutton style works for parent and not for child nodes.
Here for the togglebutton collapse and expand, i added two images(

Resources/Images/arrowexpand.png

and

Resources/Images/arrowcollapse.png

It is working perfectly with parent nodes, but not with child and subchild nodes.
For the child and subchild nodes, the default triangle button comes.
I didn't use MVVM. I don't know where I am going wrong

What I have tried:

Here is my style statements in App.xaml

<pre><Style TargetType="TreeView">
            <Setter Property="OverridesDefaultStyle" Value="True"/>
            <Setter Property="Template">
                <Setter.Value>
                    <ControlTemplate TargetType="TreeView">
                        <Border Name="Border" CornerRadius="5" BorderThickness="2">
                            <Border.BorderBrush>
                                <SolidColorBrush Color="DarkGreen"/>
                            </Border.BorderBrush>
                            <ItemsPresenter/>
                        </Border>


                    </ControlTemplate>
                </Setter.Value>
            </Setter>
        </Style>
        <Style x:Key="ExpandCollapseToggleStyle" TargetType="ToggleButton">
            <Setter Property="Focusable" Value="False"/>
            <Setter Property="Template">
                <Setter.Value>
                    <ControlTemplate TargetType="ToggleButton">
                        <Image x:Name="image" Source="Resources/Images/arrowcollapse.png" />
                        <ControlTemplate.Triggers>
                            <Trigger Property="IsChecked" Value="true">
                                <Setter TargetName="image" Property="Source" Value="Resources/Images/arrowexpand.png" />
                            </Trigger>
                        </ControlTemplate.Triggers>
                    </ControlTemplate>
                </Setter.Value>
            </Setter>
        </Style>
        <Style  x:Key="ms" TargetType="TreeViewItem" >
            <Setter Property="IsExpanded" Value="True"/>
            <Setter Property="Background" Value="Transparent"/>
            <Setter Property="Padding" Value="1,0,0,0"/>
            <Setter Property="Template">
                <Setter.Value>
                    <ControlTemplate TargetType="TreeViewItem">
                        <Grid>
                            <Grid.ColumnDefinitions>
                                <ColumnDefinition MinWidth="19" Width="Auto"/>
                                <ColumnDefinition Width="Auto"/>
                                <ColumnDefinition Width="*"/>
                            </Grid.ColumnDefinitions>
                            <Grid.RowDefinitions>
                                <RowDefinition Height="Auto"/>
                                <RowDefinition/>
                            </Grid.RowDefinitions>
                        <!--     Connecting Lines -->
                           <Rectangle x:Name="HorLn" Margin="9,1,0,0" Height="1" Stroke="#DCDCDC" SnapsToDevicePixels="True"/>
                            <Rectangle x:Name="VerLn" Width="1" Stroke="#DCDCDC" Margin="0,0,1,0" Grid.RowSpan="2" SnapsToDevicePixels="true" Fill="White"/>
                            <ToggleButton Margin="-1,0,0,0" x:Name="Expander" Style="{StaticResource ExpandCollapseToggleStyle}" IsChecked="{Binding Path=IsExpanded, RelativeSource={RelativeSource TemplatedParent}}" ClickMode="Press"/>
                            <ToggleButton Margin="-1,0,0,0" x:Name="Collapsed" Style="{StaticResource ExpandCollapseToggleStyle}" IsChecked="{Binding Path=IsExpanded, RelativeSource={RelativeSource TemplatedParent}}" ClickMode="Press"/>
                            <Border Name="Bd" Grid.Column="1" Background="{TemplateBinding Background}" BorderBrush="{TemplateBinding BorderBrush}" BorderThickness="{TemplateBinding BorderThickness}" Padding="{TemplateBinding Padding}" SnapsToDevicePixels="True">
                                <ContentPresenter x:Name="PART_Header" ContentSource="Header" HorizontalAlignment="{TemplateBinding HorizontalContentAlignment}" MinWidth="20"/>
                            </Border>
                            <ItemsPresenter x:Name="ItemsHost" Grid.Row="1" Grid.Column="1" Grid.ColumnSpan="2"/>
                        </Grid>
      
                        <!-- This trigger changes the connecting lines if the item is the last in the list -->
                       
                       <ControlTemplate.Triggers>
                            <Trigger Property="IsExpanded" Value="False">
                                <Setter TargetName="ItemsHost" Property="Visibility" Value="Collapsed"/>
                            </Trigger>
                            <Trigger Property="HasItems" Value="false">
                                <Setter TargetName="Expander" Property="Visibility" Value="Hidden"/>
                            </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 TargetName="Bd" Property="Background" Value="{DynamicResource {x:Static SystemColors.HighlightBrushKey}}"/>
                                <Setter Property="Foreground" Value="{DynamicResource {x:Static SystemColors.HighlightTextBrushKey}}"/>
                            </Trigger>
                            <MultiTrigger>
                                <MultiTrigger.Conditions>
                                    <Condition Property="IsSelected" Value="true"/>
                                    <Condition Property="IsSelectionActive" Value="false"/>
                                </MultiTrigger.Conditions>
                                <Setter TargetName="Bd" Property="Background" Value="Green"/>
                                <Setter Property="Foreground" Value="White"/>
                            </MultiTrigger>
                            <Trigger Property="IsEnabled" Value="false">
                                <Setter Property="Foreground" Value="{DynamicResource {x:Static SystemColors.GrayTextBrushKey}}"/>
                            </Trigger>
                        </ControlTemplate.Triggers>
                    </ControlTemplate>
                </Setter.Value>
            </Setter>
        </Style>

In the treeview

<pre> <TreeView x:Name="myTreeview" ItemContainerStyle="{StaticResource ms}"/>