GGBHAItester

#include<iostream>
#include<cstdio>
#include<vector>
#include<cstring>
#include<queue>
using namespace std;
vector<vector<int> >graph (100001 );
bool restr[100001];
bool visited[100001];
queue<int>Q;
long long total;
void bfs(int level)
{
  //traversal always starts with node 1
  int node;
  do
  {
    queue<int> ql;
    while(!Q.empty())
    {
      node=Q.front();
      Q.pop();
      /* if(visited[node])
        continue;*/

      visited[node]=1;

      if(restr[node])
        total+=(level*2);

      for(int i=0; i<graph[node].size(); i++ )
      {
         if(visited[graph[node][i]])
          continue;



          ql.push(graph[node][i]);
      }


    }
    Q=ql;
    level++;

  }while(!Q.empty());
}

int main()
{
  int t,n,m,a,b;
  cin>>t;
  while(t--)
  {
    cin>>n>>m;

    graph.clear();
    graph.resize(100001);
    for(int i=1;i<n;i++)
    {
      cin>>a>>b;
      graph[a].push_back(b);
      graph[b].push_back(a);
    }
    memset(restr,0,sizeof(restr));
    for(int i=0;i<m;i++)
    {
      cin>>a;
      restr[a]=1;
    }
    memset(visited,0,sizeof(visited));//all are unvisited initially

    Q.push(1);
    total=0;
    bfs(0);
    double ans=(1.0/m)*total;
    printf("%.6f\n",ans );
  }
}