( ( ( ( ( An ( ice cube ) ) , ) ( a solid ) ) , ) ( ( becomes ( ( a liquid ) ( when ( it melts ) ) ) ) . ) )
(ROOT (S (NP (NP (DT An) (NN ice) (NN cube)) (, ,) (NP (DT a) (JJ solid)) (, ,)) (VP (VBZ becomes) (NP (NP (DT a) (NN liquid)) (SBAR (WHADVP (WRB when)) (S (NP (PRP it)) (VP (VBZ melts)))))) (. .)))
An    ice cube, a solid, becomes a liquid when it melts.
(ROOT (S (NP (NN Ice) (NNS cubes)) (VP (VBP are) (NP (NP (DT an) (NN example)) (PP (IN of) (NP (NP (DT the) (JJ solid) (NN form)) (PP (IN of) (NP (NN water))))))) (. .)))
Ice cubes are an example of the solid form of water.