#include<bits/stdc++.h>
using namespace std;

using ll=long long;using ull=unsigned long long;using pii=pair<int,int>;using i128=__int128_t;
#define all(x) x.begin(),x.end()
#define mem0(x) memset(x,0,sizeof(x))
#define YES puts("YES")
#define NO puts("NO")
#define Yes puts("Yes")
#define No puts("No")
#define errorf(...) fprintf(stderr, __VA_ARGS__) 
#define endl '\n'
#define pb push_back
inline int read(){int f=1,x=0;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;}
template <class T> inline T read(){T f=1,x=0;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;}
template <class T> void write(T x){if(x<0)putchar('-'),x=-x;if(x>9)write(x/10);putchar(x%10+'0');}

using ld=double;

const int N = 1e6+5;
vector<int> G[N];
int fa[N],bdfn[N],sz[N],st[N];
int tot;

struct Node{
    ld a;
    ld taga;
}t[N*4];
void pushup(int o){
    t[o].a=t[o<<1].a+t[o<<1|1].a;
}
void upd(int o,int l,int r,ld qa){
    t[o].a+=qa*(r-l+1),t[o].taga+=qa;
}
void build(int o,int l,int r){
    t[o]={0,0};
    if(l==r)return;
    int lch=o<<1,rch=o<<1|1;
    int mid=(l+r)>>1;
    build(lch,l,mid),build(rch,mid+1,r);
}
void pushdown(int o,int l,int r){
    if(t[o].taga){
        int mid=(l+r)>>1;
        upd(o<<1,l,mid,t[o].taga);
        upd(o<<1|1,mid+1,r,t[o].taga);
        t[o].taga=0;
    }
}
void add(int o,int l,int r,int ql,int qr,ld qa){
    if(ql>qr)return;
    if(ql<=l&&r<=qr)return upd(o,l,r,qa);
    pushdown(o,l,r);
    int lch=o<<1,rch=o<<1|1;
    int mid=(l+r)>>1;
    if(ql<=mid)add(lch,l,mid,ql,qr,qa);
    if(qr>mid)add(rch,mid+1,r,ql,qr,qa);
    pushup(o);
}
ld query(int o,int l,int r,int qi){
    if(qi<l || qi>r)return 0;
    if(l==r)return t[o].a;
    pushdown(o,l,r);
    int lch=o<<1,rch=o<<1|1;
    int mid=(l+r)>>1;
    if(qi<=mid)return query(lch,l,mid,qi);
    return query(rch,mid+1,r,qi);
}

void bdfs(int u,int f){
    fa[u]=f;
    for(int v:G[u]){
        if(v==f)continue;
        bdfn[v]=++tot;
        if(!st[u])st[u]=tot;
        sz[u]++;
    }
    for(int v:G[u]){
        if(v==f)continue;
        bdfs(v,u);
    }
}

void solve(){
    int n=read(),c=read();
    for(int i=1;i<n;i++){
        int u=read(),v=read();
        G[u].push_back(v);G[v].push_back(u);
    }

    
    tot=1;bdfn[1]=1;
    bdfs(1,0);

    build(1,1,n);
    add(1,1,n,bdfn[c],bdfn[c],1);

    int m=read();
    
    ld ans = 0;
    for(int i=1;i<=m;i++){
        int x=read();
        auto a = query(1,1,n,bdfn[x]);
        ans += a;
        add(1,1,n,bdfn[x],bdfn[x],-a);


        if(sz[x]+(fa[x]!=0)==0){
            puts("???");
        }
        else a /= (sz[x]+(fa[x]!=0));

        if(sz[x])add(1,1,n,st[x],st[x]+sz[x]-1,a);
        if(fa[x])add(1,1,n,bdfn[fa[x]],bdfn[fa[x]],a);
    }

    for(int i=1;i<=n;i++)G[i].clear(),sz[i]=0;

    printf("%.8f\n",ans);
}

int main(){
    int T=read();
    while(T--)solve();
    return 0;
}