python - Importing modules from nested folder

I have a folder structure like this

main_folder
|
|--done
|  |
|  |--test1
|  |--__init__.py

|
|---check.py

__init__.py:

class Tries(object):
    def __init__(self):
        print "Test"

check.py:

from done.test1 import Tries
Tries()

Error:

---------------------------------------------------------------------------

ImportError                               Traceback (most recent call last)
 in ()
----> 1 from done.test1 import Tries

ImportError: No module named done.test1 

I am not able to import modules from the nested folder. Is there any way to do this.

Edit:

After Salva's answer I changed my structure like this

.
├── check.py
|--__init__.py(no content)
└── done
    ├── __init__.py(no content)
    └── test1
        └── __init__.py <-- this files contains your Tries class

Same error is thrown now also.

Answer

You need a file __init__.py in each directory you want it to be considered a package so you need it in both directories:

.
├── check.py
└── done
    ├── __init__.py

    └── test1
        └── __init__.py <-- this files contains your Tries class