go test -bench .
ok, starting
BenchmarkImmutableAvlTreeLevelDB2-4     ok, starting
ok, starting
    2000      813477 ns/op
ok, starting
BenchmarkImmutableAvlTreeMemDB-4        ok, starting
ok, starting
   10000      104649 ns/op
PASS
ok    github.com/tendermint/go-merkle 229.565s
