Attached property to move a part of TreeViewItem to the edge of TreeView with a specified left margin

TreeViewHelper.cs

using System.Windows;
using System.Windows.Controls;
using System.Windows.Media;

public static class TreeViewHelper
{
    public static double? GetLeftMargin(DependencyObject obj)
    {
        return (double?)obj.GetValue(LeftMarginProperty);
    }
    public static void SetLeftMargin(DependencyObject obj, double value)
    {
        obj.SetValue(LeftMarginProperty, value);
    }
    public static readonly DependencyProperty LeftMarginProperty =
        DependencyProperty.RegisterAttached("LeftMargin", typeof(double?), typeof(TreeViewHelper), new PropertyMetadata(null, OnValueChanged));

    private static void OnValueChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
    {
        if ((d is FrameworkElement element) && (e.NewValue is double leftMargin))
        {
            element.Loaded += (_, _) =>
            {
                TreeView? tv = GetTreeView(element);
                if (tv is null)
                    return;

                Point relativePosition = element.TransformToAncestor(tv).Transform(new Point(0, 0));
                element.RenderTransform = new TranslateTransform(leftMargin - relativePosition.X, 0);
            };
        }
    }

    private static TreeView? GetTreeView(FrameworkElement element)
    {
        DependencyObject test = element;
        while (test is not null)
        {
            test = VisualTreeHelper.GetParent(test);
            if (test is TreeView tv)
                return tv;
        }
        return null;
    }
}