To make stars appear larger without trails, you generally need to increase their apparent size or brightness rather than use a longer exposure alone. Based on the answers, a softening filter can help spread each star’s light over a slightly larger area, which can also make star colors show more clearly.

A higher ISO may also help record more stars and color, but it increases noise and can make sky glow more noticeable, especially near towns or cities. Shooting in RAW is important so you can experiment with ISO and recover the best balance of detail, color, and noise in post-processing.

If you want longer exposures without star trails, use a tracking mount. That lets the camera follow the stars so you can keep them sharp during longer exposures.

A graduated ND filter was mentioned for reducing brighter foreground/sky glow effects, but its usefulness here is uncertain and may complicate exposure.

In short: try RAW, experiment with ISO, consider a softening filter for the enlarged-star look, and use a tracking mount if you need longer exposures without trails.