As you are bound to know by now, a tree is a connected graph
consisting of N vertices and N−1 edges. Trees also have the property
of there being exactly a single unique path between any pair of
vertices.
You will be given a tree in which every edge is assigned a weight –
a non negative integer. The weight of a path is the product of the
weights of all edges on the path. The weight of the tree is the sum of
the weights of all paths in the tree. Paths going in opposite
directions (A to B and B to A) are considered the same and, when
calculating the weight of a tree, are counted only once.
Write a program that, given a tree, calculates its weight modulo 1000000007.
