樹上差分板子：

#include <cmath>
#include <cstdio>
#include <cstring>
#include <iostream>
#include <algorithm>
#define db double
#define sg string
#define ll long long
#define rep(i,x,y) for(ll i=(x);i<=(y);i++)
#define red(i,x,y) for(ll i=(x);i>=(y);i--)
using namespace std;

const ll N=5e4+5;
const ll Inf=1e18;

ll n,m,ans,v[N],dep[N],fa[N][20];
ll cnt,to[N<<1],nxt[N<<1],head[N];

inline ll read() {
    ll x=0;char ch=getchar();bool f=0;
    while(ch>'9'||ch<'0'){if(ch=='-')f=1;ch=getchar();}
    while(ch>='0'&&ch<='9'){x=(x<<1)+(x<<3)+ch-'0';ch=getchar();}
    return f?-x:x;
}

inline void write(ll x) {
	if(x<0) putchar('-');
	if(x>9) write(x/10);
	putchar(x%10+48);
}

void ins(ll x,ll y) {
	to[++cnt]=y;nxt[cnt]=head[x];head[x]=cnt;
}

void dfs(ll x) {
	dep[x]=dep[fa[x][0]]+1;
	rep(i,1,19) fa[x][i]=fa[fa[x][i-1]][i-1];
	
	for(ll i=head[x];i;i=nxt[i]) {
		ll y=to[i];
		if(y!=fa[x][0]) {
			fa[y][0]=x;dfs(y);
		}
	}
}

ll lca(ll x,ll y) {
	if(dep[x]<dep[y]) swap(x,y);
	
	ll dlt=dep[x]-dep[y];
	
	rep(i,0,19) if(dlt&(1<<i)) x=fa[x][i];
	
	if(x==y) return y;
	
	red(i,19,0) if(fa[x][i]!=fa[y][i]) x=fa[x][i],y=fa[y][i];
	
	return fa[x][0];
}

void _dfs(ll x) {
	for(ll i=head[x];i;i=nxt[i]) {
		ll y=to[i];
		if(y!=fa[x][0]) {
			_dfs(y);v[x]+=v[y];
		}
	}
	ans=max(ans,v[x]);
}

int main() {
	n=read(),m=read();
	
	rep(i,2,n) {
		ll x=read(),y=read();
		ins(x,y),ins(y,x);
	}
	
	dfs(1);
	
	rep(i,1,m) {
		ll x=read(),y=read(),z=lca(x,y);
		++v[x],++v[y];
		--v[z],--v[fa[z][0]];
	}
	
	_dfs(1);
	
	write(ans);

	return 0;
}