Let T be a tree with red and green vertices where each vertex v has its color preloaded in v$.$color. For

simplicity, let the root of T ne red. Vertex v is the root of a maximal green subtree if v is green, and its parent

is red. The vertices in the green subtree rooted by such a v are all vertices w that $($equal v$)$ or are descendants

of v$,$ and the path from v to w only contains green vertices $($which implies that w is also green$).$ Alternatively,

these trees are the connected structures that remain if we remove all read vertices and their connecting edges

from T$.$