  With the growing commercial interest in blockchain, permissioned
implementations have received increasing attention. Unfortunately, existing BFT
consensus protocols that are the backbone of permissioned blockchains, either
scale poorly or offer limited throughput. Most of these algorithms require at
least one process to receive and validate the votes from all other processes
and then broadcast the result, which is inherently non-scalable. Some
algorithms avoid this bottleneck by using aggregation trees to collect and
validate votes. However, to the best of our knowledge, such algorithms offer
limited throughput and degrade quickly in the presence of faults. In this paper
we propose \thesystem, the first BFT communication abstraction that organizes
participants in a tree to perform scalable vote aggregation and that, in faulty
runs, is able to terminate the protocol within an optimal number of
reconfigurations ($f+1$). We define precisely which aggregation trees allow for
optimal reconfiguration and show that, unlike previous protocols, when using
these configurations, \thesystem scales to large number of processes and
outperforms HotStuff's throughput by up to 38x.
