Designing the tree
list [ 1 ] . push_back ( 2 ) ; list [ 2 ] . push_back ( 1 ) ; list [ 1 ] . push_back ( 3 ) ; list [ 3 ] . push_back ( 1 ) ; list [ 2 ] . push_back ( 4 ) ; list [ 4 ] . push_back ( 2 ) ; list [ 3 ] . push_back ( 5 ) ; list [ 5 ] . push_back ( 3 ) ;