use from future.utils import iteritems then for k, v in iteritems(d) instead of for k, v in d.items()cf these best practices since it is more efficient
use from future.utils import python_2_unicode_compatible instead of copying it in treelib.tree module
I see two potential improvements:
from future.utils import iteritemsthenfor k, v in iteritems(d)instead offor k, v in d.items()cf these best practices since it is more efficientfrom future.utils import python_2_unicode_compatibleinstead of copying it intreelib.treemodule