Or search: economist
1 Syllable: S
Rep
2 Syllables: SU
beverage, hemorrhage, leverage
3 Syllables: SUU
crevices, decorative, equipage, menaces, narrative, necklaces, negative, prefaces, relative, sedative, terraces, threatenings
4 Syllables: USUU
competitive, correlative, imperative
5 Syllables: UUSUU
representative

Found 20 words across 5 groupings. Skipped 6 excess words of a similar stem.