6 4
1 2 20
2 5 100
2 3 20
6 3 70
4 1 10

by the way : before you　use the dynamic programming on the tree structure, be sure you have build the tree correctly. That's why I got WA.

Source Code is available at :
ecnu_zp@yahoo.cn

Many Thanks!

I guess this test is incorrect, because of statement:
" any biparous branch splits up to exactly two new branches", but node 3 has only one branch.

As I can see here is 2 possible trees.
1 and 3 can be root
   6
    \
  5  3
   \ /
4  2
 \ /
  1

   4
    \
  5  1
   \ /
6  2
 \ /
  3

Edited by author 20.12.2015 15:47

wrong test case, there will always be zero or two children of any node.

Thank you for your data