Infected Trees Invading My Home

I bought a new plant about a month ago and it's nearly dead. It was a $40 tree that I carried home 8 blocks. It wasn't terribly heavy, but I couldn't carry it against my body since I would have gotten dirt and mud all over my shirt, so I had to hold it away from myself while walking. It was exhausting, and I had to lay on the couch trying to get my back to chill out through 10 minutes of muscle spasms. A bit humiliating since the plant was so lightweight, but it was awkward. A week after I carried it home, my house was infested with gnats. I blamed the awful store that sold me the plant, but when I opened up my potting soil to repot my tree and get rid of the gnat eggs, a swarm of gnats came out. The infested soil? A big box store a car ride away from my house. There's a lesson in there somewhere.