Or search: worrying, troubling, worrisome, disturbing, perturbing, distressing
2 Syllables: SU
bestial, Bethel, devil, Ethel, ethyl, festal, level, levelled, levels, methyl, nestle, pestle, restful, revel, revelled, revels, special, vessel, vestal, wrestle
3 Syllables: USU
ancestral, celestial, dishevelled, especial, orchestral, successful, terrestrial
4 Syllables: UUSU
unsuccessful

Found 28 words across 3 groupings. Skipped 6 excess words of a similar stem.