( ( ( One event ) ( attracting another ) ) . )
(ROOT (NP (NP (CD One) (NN event)) (VP (VBG attracting) (NP (DT another))) (. .)))
One event attracting another.
(ROOT (S (NP (JJ Opposite) (NNS charges)) (VP (VBP attract) (NP (CD one) (DT another))) (. .)))