Optimizely Graph .NET -- Try to add fragment

I am trying to create a query with fragment and hopefully to get the query like this. 

query ArticleListing {
  ArticlePage {
    items {
      Name
      Url
      Title
      PreviewImage {
        Expanded {
          ...Image
        }
      }
    }
    total
  }
}
fragment Image on ImageFile {
  Name
  Url
  Title
  Width
  Height
}

I have a code below so far

            var fragmentImage = new FragmentBuilder<ImageFile>("Image").Fields(x => x.Name
                                                                                , x => x.Url
                                                                                , x => x.Title
                                                                                , x => x.Width
                                                                                , x => x.Height);
            articleQuery = articleQuery
                                .Fields(x => x.Name, x => x.Url, x => x.Title)
                                .Field(x => x.PreviewImage.Expanded).AddFragments(fragmentImage);

But it puts the "...Image" outside the PreviewImage.Expanded

query ArticleListing {
  ArticlePage {
    items {
      Name
      Url
      Title
      PreviewImage {
        Expanded
      }
      ...Image
    }
    total
  }
}
fragment Image on ImageFile {
  Name
  Url
  Title
  Width
  Height
}

Is there a way to make fragment to be in the PreviewImage.Expanded ?