#include<bits/stdc++.h>
#define INF 2147483647LL
#define int long long
#define MAXN 5000005
#define mod 1000000007
#define PI 3.14
#define eps 1e-10
#define pa pair<int,int>
#define ms(a,x) memset(a,x,sizeof(a))
#define mc(ar1,ar2) memcpy(ar1,ar2,sizeof(ar2))
#define mkp(a,b) make_pair(a,b)
#define ls (p<<1)
#define rs (p<<1|1)
#define fn(i,st,ed) for(int i=st;i<=ed;++i)
#define fd(i,st,ed) for(int i=st;i>=ed;--i)
#define fg(i,x,head,e) for(int i=head[x];~i;i=e[i].nxt)
using namespace std;
inline int read(){int x=0,f=1;char c=getchar();while(!isdigit(c)){if(c=='-')f=-1;c=getchar();}while(isdigit(c)){x=x*10+c-'0';c=getchar();}return x*f;}
struct edge{int to,nxt;}e[MAXN<<1];
int head[MAXN],ecnt=-1;
inline void insert(int x,int y){e[++ecnt]={y,head[x]};head[x]=ecnt;}
double p[MAXN],lz[MAXN],d[MAXN];
void solve(){
    ecnt=-1;
    int n,c;cin>>n>>c;
    fn(i,0,n)head[i]=-1,p[i]=lz[i]=0;
    p[c]=1;
    fn(i,1,n-1){
        int x,y;cin>>x>>y;
        insert(x,y);insert(y,x);
        d[x]++,d[y]++;
    }
    int m,lst=0;cin>>m;
    double ans=0;
    fn(i,1,m){
        int x;cin>>x;
        //cout<<1<<' '<<x<<' '<<p[x]<<' '<<lz[x]<<endl;
        ans+=p[x]+lz[lst];
        lz[x]+=(p[x]+lz[lst])/d[x];
        p[lst]+=p[x]/d[x];
        p[x]=0;
        lst=x;
        //cout<<2<<' '<<x<<' '<<p[x]<<' '<<lz[x]<<endl;
        //cout<<ans<<endl;
    }
    cout<<setprecision(8)<<ans<<endl;
}
signed main(){
    ios::sync_with_stdio(false);cin.tie(0);cout.tie(0);
    int T;cin>>T;
    while(T--){solve();}
    return 0;
}