How to show dynamic UMG class in Hierarchy?

Here is how I add new GridPanel to my custom UUserWidget class.

bool UInventoryWidget::Initialize()
{
	Super::Initialize();

	UCanvasPanel* RootWidget = Cast<UCanvasPanel>(GetRootWidget());
	if (WidgetTree && RootWidget)
	{
		if (GridPanel == nullptr)
		{
			GridPanel = WidgetTree->ConstructWidget<UGridPanel>(UGridPanel::StaticClass(), TEXT("GridPanel"));

			UCanvasPanelSlot* GridPanelSlot = RootWidget->AddChildToCanvas(GridPanel);
			GridPanelSlot->SetAnchors(FAnchors(0.f, 0.f, 1.f, 1.f));
		}
	}

	return true;
}

When I open Blueprint associated with my custom UUserWidget class I see in editor that grid panel was rendered but I don’t see in in Hierarchy widow. How to fix this?