木 - tree
伸びる - grow, stretch, grow longer
木の場合はgrow taller, get taller, get biggerになります
伸びきった木 - the tree has gotten bigger, the tree has grown taller
家の隣に生えている木の枝が伸びきっていて邪魔なので、早く切って欲しい
The branches on the tree next door has gotten longer and they are in the way so I want them to cut them quickly