Is it a tree

#include "bits/stdc++.h"
using namespace std;
const int N = 2e4;
int  vis[N], c = 0;
vector < vector < int > > v(N);

void dfs(int root , int check){
    vis[root] = 1;

    for(auto it : v[root]){
        if(!vis[it])dfs(it, root);
        else if(vis[it] && it != check){
            c = 1;
            return;
        }
    }
}
int main(){
    int i, l, r;

    int n, m;
    cin >> n >> m;
    for( i = 0; i < m; i++){
        cin >> l >> r;
       v[l].push_back(r);
       v[r].push_back(l);
    }
 //   for(i = 1; i <= n; i++)cout << parent[i] << ' ';cout << '\n';
 dfs(1,1);
    for(i = 1; i <= n; i++){
    if(!vis[i])c++;
    }
  //  cout << c << endl;
    if(c || m != n-1)return cout << "NO",0;
    cout << "YES";
}