( It ( ( is ( made ( by ( ( ( reacting ( sulfur trioxide ) ) ( with ( sulfuric acid ) ) ) ( to ( produce oleum ) ) ) ) ) ) . ) )
(ROOT (S (NP (PRP It)) (VP (VBZ is) (VP (VBN made) (PP (IN by) (S (VP (VBG reacting) (NP (NN sulfur) (NN trioxide)) (PP (IN with) (NP (JJ sulfuric) (NN acid))) (S (VP (TO to) (VP (VB produce) (NP (NN oleum)))))))))) (. .)))
It is made by reacting sulfur trioxide with sulfuric acid to produce oleum.
(ROOT (S (NP (NNP Sulfur)) (VP (MD can) (VP (VB combine) (PP (IN with) (NP (NN oxygen))) (S (VP (TO to) (VP (VB produce) (NP (NN sulfur) (NN trioxide))))))) (. .)))