。
The trees are budding.
Literal
Trees [on-に] buds [subject-が] are-coming-out.
芽が出る ('buds come out') uses the intransitive 出る, with the buds themselves as subject and the trees marked with locative に. The transitive partner 芽を出す treats the trees as active subjects, but here Japanese frames the budding as a spontaneous event happening to the trees rather than performed by them. Japanese routinely toggles between transitive and intransitive partners depending on whether the action is presented as agent-driven or natural.