NavigationViewItem does not render MenuItems beyond the 2nd nesting level

Describe the bug

When nesting NavigationViewItem.MenuItems three or more levels deep in a NavigationView with PaneDisplayMode="Left", only the first two levels are rendered and expandable. Level 3+ items are never displayed, even though they are correctly present in the data (MenuItems.Count confirms this via debugging), and even when IsExpanded = true is explicitly set on the level-2 parent item.

To Reproduce

new NavigationViewItem
{
    Content = "Level 1",
    MenuItems =
    {
        new NavigationViewItem
        {
            Content = "Level 2",
            MenuItems =
            {
                new NavigationViewItem
                {
                    Content = "Level 3", // never rendered
                    TargetPageType = typeof(SomePage),
                }
            }
        }
    }
}

Expected behavior

NavigationViewItem should support at least the same nesting behavior recursively at any depth, or the limitation should be explicitly documented.

Screenshots

OS version

Windows 11

.NET version

.NET 8

WPF-UI NuGet version

4.3.0

Additional context

No response