How to import .py file from another directory in animationnodes2.1? I am writing a custom node in animation nodes2.1,and i wanted to import .py file from another directory as a module,for example,i have two directories:  

../nodes/my_nodes/test.py

../nodes/bvh_tree/construct.py


i wanted to import construct.py to my test.py,i tried this code:

from ..bvh_tree import construct
from construct import ConstructBVHTreeNode


but failed,the consoul gave me "no moule named construct",i was confused about the error,how to fix this problem? i had tried the way on the topic stackoverflow.com,but can not work still,anyone has an idea,Thanks in advanced!
Th import statement should be:

from .. bvh_tree.construct import ConstructBVHTreeNode


Because the from import takes the form from module import something.