Simple process and useful product.
You can grow Peppermint in your window garden or outdoors in spring / summer. It will self-propagate (has no respect for garden boundaries) so if you plant outside, be ready to spend some time weeding out the unwanted growth.
http://www.askaprepper.com/make-peppermint-oil-best-insect-repellent/There are good pictures showing the steps and ingredients.
Yes, it does repel insects, but may need to be reapplied as it evaporates.