( ( ( This type ) ( of digestion ) ) ( ( ( ( begins ( in ( the ( ( mouth and ) stomach ) ) ) ) but ) ( ( occurs mainly ) ( in ( the ( small intestine ) ) ) ) ) . ) )
(ROOT (S (NP (NP (DT This) (NN type)) (PP (IN of) (NP (NN digestion)))) (VP (VP (VBZ begins) (PP (IN in) (NP (DT the) (NN mouth) (CC and) (NN stomach)))) (CC but) (VP (VBZ occurs) (ADVP (RB mainly)) (PP (IN in) (NP (DT the) (JJ small) (NN intestine))))) (. .)))
This type of digestion begins in the  mouth and stomach but occurs mainly in the small intestine.
(ROOT (S (NP (DT The) (JJ small) (NN intestine)) (VP (VBZ begins) (PP (IN in) (NP (DT the) (NN stomach)))) (. .)))