Why are some GameObjects rendered like PNGs under my Render Texture?

Hey Unity,

So, I made a retro-looking texture for my game. If you want to see the exact steps I followed, here's a link to the one-minute video I used to make the texture: https://www.youtube.com/watch?v=gdUhzNnNuwo

Okay, so the texture works fine and well, but for some reason, certain GameObjects (mainly the trees I'm using: Realistic Tree 9 [Rainbow Tree] asset by Pixel Games) act like a PNG image (or like a green screen or something). Basically, they don't have they're original texture and it's made a PNG for some odd reason. So, If I play-test my game, when the SceneManager loads the scene with the trees on it, they display the UI of the previous scene instead of the tree texture. I don't know if this is because of the render texture or not, but I am very new to programming, so I can't diagnose the issue myself.

Here's a picture of what I'm talking about.

Those PNG parts are my trees. And when I play the scene, they render parts of a previous scene or a random material. Any help would be VERY appreciated. Thank you in advance, and stay safe :-)