create undirected edges initialize the tree given in the diagram
v [ 1 ] . push_back ( 2 ) , v [ 2 ] . push_back ( 1 ) ; v [ 1 ] . push_back ( 3 ) , v [ 3 ] . push_back ( 1 ) ; v [ 1 ] . push_back ( 4 ) , v [ 4 ] . push_back ( 1 ) ; v [ 2 ] . push_back ( 5 ) , v [ 5 ] . push_back ( 2 ) ; v [ 2 ] . push_back ( 6 ) , v [ 6 ] . push_back ( 2 ) ; v [ 3 ] . push_back ( 7 ) , v [ 7 ] . push_back ( 3 ) ; v [ 4 ] . push_back ( 8 ) , v [ 8 ] . push_back ( 4 ) ; v [ 4 ] . push_back ( 9 ) , v [ 9 ] . push_back ( 4 ) ; v [ 4 ] . push_back ( 10 ) , v [ 10 ] . push_back ( 4 ) ; v [ 5 ] . push_back ( 11 ) , v [ 11 ] . push_back ( 5 ) ; v [ 5 ] . push_back ( 12 ) , v [ 12 ] . push_back ( 5 ) ; v [ 7 ] . push_back ( 13 ) , v [ 13 ] . push_back ( 7 ) ; v [ 7 ] . push_back ( 14 ) , v [ 14 ] . push_back ( 7 ) ;