IQueryable.Union/Concat in .net core 3

I was able to achieve it with the following code:

IQueryable<Geography> geographies = _unitOfWork.GeographyRepository.GetAll().Select(o => new Geography { Id = o.Id, Name = o.Name });

IQueryable<Geography> dummyGeographies = _unitOfWork.GeographyRepository.GetAll().Select(o => new Geography { Id = -1, Name = "All" });

var combinedGeographies = geographies.Union(dummyGeographies);