( It ( ( ( will only ) ( burn ( if ( ( ( the substrata ) ( under it ) ) ( , ( ( for ( example wood ) ) ( , ( are burning ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (PRP It)) (VP (MD will) (ADVP (RB only)) (VP (VB burn) (SBAR (IN if) (S (NP (NP (DT the) (NN substrata)) (PP (IN under) (NP (PRP it)))) (, ,) (PP (IN for) (NP (NN example) (NN wood))) (, ,) (VP (VBP are) (VP (VBG burning))))))) (. .)))
It will only burn if the substrata under it, for example wood, are burning.
(ROOT (S (NP (NNP Wood) (NNP burning)) (VP (VBZ is) (NP (NP (DT an) (NN example)) (PP (IN of) (NP (NP (DT a) (JJ different) (NN substance)) (VP (VBG being) (VP (VBN formed))))))) (. .)))