TypeError in tree_cluster_hist.py recirsive tree traversal

[heikomuller]

I get the following error when running https://github.com/diana-hep/TreeNiN/blob/master/code/top_reference_dataset/toptag_reference_dataset_Tree.py:

TypeError: list indices must be integers or slices, not float

It appears that the error occurs at

TreeNiN/code/top_reference_dataset/tree_cluster_hist.py

Line 44 in bb67898

id=len(tree)/2

My fix is to cast the value of the division to int, i.e.,

id = int(len(tree)/2)

Note: I'm using Python 3.7 instead of 2.7