Use tree reduce for aggregation
Use tree reduce for aggregation

kcompher/thunder,jwittenbach/thunder,kunallillaney/thunder,mikarubi/thunder,poolio/thunder,oliverhuangchao/thunder,thunder-project/thunder,kunallillaney/thunder,j-friedrich/thunder,poolio/thunder,j-friedrich/thunder,oliverhuangchao/thunder,zhwa/thunder,mikarubi/thunder,pearsonlab/thunder,kcompher/thunder,zhwa/thunder,pearsonlab/thunder