Add treeinterface benchmarks
```
nCPU: 4, nLeafs: 10000
asmtree.Add loop: 1m33.393613916s
asmtree.AddBatch: 480.164271ms
gravitontree.Add loop: 10.127451689s
gravitontree.AddBatch: 141.29108ms
arbo.Add loop: 1.16466211s
arbo.AddBatch: 97.870759ms
nCPU: 8, nLeafs: 10000
asmtree.Add loop: 24.538163095s
asmtree.AddBatch: 194.14454ms
gravitontree.Add loop: 6.150883978s
gravitontree.AddBatch: 90.742666ms
arbo.Add loop: 600.259558ms
arbo.AddBatch: 50.440291ms
---
nCPU: 4, nLeafs: 500000
asmtree.AddBatch: 24.95076993s
gravitontree.AddBatch: 11.768588412s
arbo.AddBatch: 23.360363426s
nCPU: 8, nLeafs: 500000
asmtree.Add loop: (not executed)
asmtree.AddBatch: 14.363474201s
gravitontree.Add loop: 8m45.300930089s
gravitontree.AddBatch: 7.377581508s
arbo.Add loop: 2m0.229851504s
arbo.AddBatch: 8.759028338s
```