django-values-nested-tree.py

from app.models import SomeModel
from collections import defaultdict


def tree_from_values(queryset, parent_field_id):
    root = defaultdict(lambda: defaultdict(list))
    for d in queryset:
        # no need to pop but we don't need it anyway
        parent = d.pop(parent_field_id)
        pk = d['pk']
        root[pk].update(d)
        root[parent]['_children'].append(root[pk])

    return root[None]


queryset = SomeModel.objects.values('pk', 'parent_id', 'some_other_field')
roots = tree_from_values(queryset, 'parent_id')['_children']