Importing own Python package from git

I have the following python package created by myself:

C:.
│   .gitignore
│   MANIFEST
│   setup.py
│
├───.vscode
│   │   settings.json
│   │
│   └───.ropeproject
│           config.py
│           objectdb
│
├───calendarlib
│   │   __init__.py
│   │
│   ├───cal
│   │   │   cal.py
│   │   │   event.py
│   │   │   __init__.py
│   │   │
│   │   └───__pycache__
│   │           cal.cpython-36.pyc
│   │           calendar.cpython-36.pyc
│   │           event.cpython-36.pyc
│   │           __init__.cpython-36.pyc
│   │
│   ├───database
│   │   │   db.py
│   │   │   __init__.py
│   │   │
│   │   └───__pycache__
│   │           db.cpython-36.pyc
│   │           __init__.cpython-36.pyc
│   │
│   └───ui
│           window.py
│           __init__.py
│
├───calendarlib.egg-info
│       dependency_links.txt
│       PKG-INFO
│       SOURCES.txt
│       top_level.txt
│
└───dist
        calendarlib-0.1.tar.gz
        calendarlib-0.2.tar.gz

__init__s are empty. Now when I use this code like with creating main.py here and importing stuff, it works. But when I push it to my git repo, install it with: pip install -U git+https://github.com/frynio/calendarlib (it is present in site-packages in Python installation dir) and do something like this:

import sys
from calendarlib.ui import window

if __name__ == '__main__':
    app = window.QApplication(sys.argv)
    foo = window.CalendarWindow()
    foo.show()
    sys.exit(app.exec_())

It says:

Traceback (most recent call last):
  File "main.py", line 2, in <module>
    from calendarlib.ui import window
  File "C:\Python36\lib\site-packages\calendarlib\ui\window.py", line 4, in <module>
    from database import db
ModuleNotFoundError: No module named 'database'

The code is in here.

What can I do? Should I import it somehow different in my app, or should I change imports in calendarlib itself?