So this is my third year film! Since the two people I've talked about it to said it's a good idea but very obscure, I'll explain it.
The story is a person and a tree co-exist in this world where most things have been destroyed by toxic waste and other stuff. The sea level has risen and comprises of some acidic substance and the air is too polluted to inhale. Thus this person walks around in a space suit (the masking tape patches are from accidentally falling into acid, I imagine) and relies on an oxygen tank to breathe. The way the oxygen tank works is -- throughout the day, the person breathes the oxygen in the tank and exhales carbon dioxide and water back into it. When the oxygen level is too low, the person goes back into the lab-cave and replaces it into these tubes hanging from the ceiling -- which connects to a tree that stands on top of the cave. The tree is mostly machine, and has been engineered to release any oxygen it produces during photosynthesis into the tank, where it becomes breathable air. Meanwhile, when the tank filled with carbon dioxide and water is hooked up to the tubes, the tree uses it for its own life functions.
There's another tank already full of oxygen from the last tank exchange the person did with the tree. The person then uses this tank to go about their...daily activities, which I imagine is just wandering around the nearby landscape until they need to refill again. The person has been here so long that they've started drawing the landmarks they know of on the backs of these tree maintenance checklists, a process which they've neglected. As a result (or perhaps it was inevitable) the tree stops 'working' and the person returns to the lab-cave to find there is no oxygen left. They hurry up to try to fix the tree, but to no avail. And then they die.
In an old version of the story I had this poor soul just barely manage to resuscitate the tree and happen to find a pod of seeds the tree had managed to produce -- something they would have discovered earlier if they'd bothered with more frequent tree maintenance. But I thought that was another story. And mostly I didn't have time. I sort of want to redo this idea with a clearer and better overall story but eh.