I get an unresolved reference error when I try to use the package

Question

i tried to use example1.py as a package but i got unresolved reference error. how can i fix the error.

you can see below the folder structure:

PycharmProjects
├── first_folder
│   └── example1.py
│       __init__.py
└── second_folder
    └── example2.py

# example1.py
def example_1():
  return None

# example2.py
import sys
sys.path.append('/home/user/PycharmProjects/')
from first_folder.example1 import example_1
# i am getting an error at above part