Before Christmas, our whole family enjoys tree-trimming with lights and small decorations.

tree-trimming 是由 tree（树）和 trimming（装饰）组成的复合名词。trim 本意是"修剪"，加上 -ing 后缀表示"装饰的动作"，tree-trimming 特指"装饰圣诞树"的传统活动。