def __bisect__(t,e):
# e = __find_centroid_edge__(t)
u = e.tail_node
v = e.head_node
u.remove_child(v)
t1 = Tree(seed_node = v)
if u.num_child_nodes() == 1:
p = u.parent_node
v = u.child_nodes()[0]
l_v = v.edge_length
u.remove_child(v)
if p is None: # u is the seed_node; this means the tree runs out of all but one side
t.seed_node = v
return t,t1
l_u = u.edge_length
p.remove_child(u)
p.add_child(v)
v.edge_length = l_u+l_v
u = p
while u is not None:
__updateNode__(u)
u = u.parent_node
t.annotated = True
t1.annotated = True
return t,t1
