Possible Opposites based on different aspects:
* Structure: Bush/Shrub - Unlike trees, they are generally shorter and have multiple stems growing from the ground.
* Growth: Grass/Flower - These are smaller plants that typically don't grow as tall or have a single, woody trunk.
* Material: Stone/Metal/Plastic - These are inanimate materials that are not living organisms like trees.
* Location: Sky/Ocean/Desert - These are environments where trees typically don't thrive.
* Function: Building/Structure - A building serves a practical purpose, while a tree is typically for ecological reasons.
It's important to consider the context of the question to determine the most fitting opposite.