Complex sentence: After graduating with his B.A. and M.A., Xu went to the United States to pursue a PhD at the University of California at Berkeley, where we was a core member of Berkeley's Text Retrieval Conference (TREC) competition team.
Split into simpler sentences: After graduating with B.A. and M.A., Xu went to the United States to pursue a PhD at the University of California at Berkeley. He was a core member of Berkeley's Text Retrieval Conference (TREC) competition team.