Complex sentence: Native Sikkimese refers to indigenous peoples of Sikkim, including Lepchas and Bhutias, compared to (newly) immigrant Sikkimese, referring to Nepali people and Tibetan people.
Split into simpler sentences: Native Sikkimese refers to indigenous peoples of Sikkim, including Lepchas and Bhutias. This is a concept to compare with (newly) Immigrant Sikkimese, which refers to Nepali people and Tibetan people.