Expand tree when mouse is over using event triggers

Now idea is to expand tree items after some period of time.

XAML:

<Window x:Class="TreeViewMouseOverExpand.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:viewModel="clr-namespace:TreeViewMouseOverExpand.ViewModel"
        xmlns:treeViewModel="clr-namespace:TreeViewMouseOverExpand.Model"
        Title="MainWindow" Height="350" Width="525">
    <Grid>
        <Grid.Resources>
            <viewModel:TreeViewMouseOverExpandViewModel x:Key="TreeViewMouseOverExpandViewModel" />
        </Grid.Resources>
        
        <TreeView DataContext="{StaticResource TreeViewMouseOverExpandViewModel}" ItemsSource="{Binding TreeViewMouseOverExpandItems}">

            <TreeView.ItemContainerStyle>
                <Style TargetType="TreeViewItem">
                    <Style.Triggers>
                        <EventTrigger RoutedEvent="MouseEnter">
                            <EventTrigger.Actions>
                                <BeginStoryboard>
                                    <Storyboard>
                                        <BooleanAnimationUsingKeyFrames 
                                            Duration="00:00:01" 
                                            Storyboard.TargetProperty="(TreeViewItem.IsExpanded)">
                                            <DiscreteBooleanKeyFrame Value="True" />
                                        </BooleanAnimationUsingKeyFrames>
                                    </Storyboard>
                                </BeginStoryboard>
                            </EventTrigger.Actions>
                        </EventTrigger>
                    </Style.Triggers>
                </Style>
            </TreeView.ItemContainerStyle>            
            
            <TreeView.ItemTemplate>

                <HierarchicalDataTemplate ItemsSource="{Binding Children}" DataType="{x:Type treeViewModel:TreeViewMouseOverExpandModel}">
                    <TreeViewItem Header="{Binding Name}">

                    </TreeViewItem>

                </HierarchicalDataTemplate>

            </TreeView.ItemTemplate>

        </TreeView>
    </Grid>
</Window>

Example download from here.

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Problem with above example is that after executing event trigger you will not be able to change any property (that means that expand / collapse will not work anymore). Solution is in FillBehavior="Stop" (see How to: Set a Property After Animating It with a Storyboard), but, I wouldn't write this article if there is no at least one "but" :), I didn't find proper solution, until now, problem is that if you FillBehavior="Stop" in MouseEnter then trigger will not work at all... if you implement MouseLeave trigger with FillBehavior="Stop", then it will partly work with strange behavior...

In my case, for our product I implemented TreeViewItem.PreviewDragEnter (without FillBehavior="Stop"), and then TreeViewItem.MouseLeave with FillBehavior="Stop", so I have two different triggers on which I could respond... but for MouseEnter / MouseLeave I don't have clear idea how to do it without some hacking in code behind...