The phrase "bushes up" is often used to describe the act of thickening or increasing the density of something, such as a shrub or a plant. Synonyms for this phrase include "densifies," "thickens," or "fills out." These words illustrate an act of packing together or adding more material to augment what already exists. Other synonyms for "bushes up" include "enlarges," "expands," and "extends," which embody the idea of making something larger in size or scope. Overall, these words all convey the idea of adding more substance or size to something that already exists, which is what it means to "bush up".