@ApiStatus.Internal
  public CustomRegionTreeElement createNestedRegion(@NotNull PsiElement element) {
    if (mySubRegions == null) mySubRegions = new ArrayList<>();
    CustomRegionTreeElement currSubRegion = new CustomRegionTreeElement(element, myProvider, this);
    mySubRegions.add(currSubRegion);
    return currSubRegion;
  }
@ApiStatus.Internal
  public CustomRegionTreeElement createNestedRegion(@NotNull PsiElement element)