Connect mongo shows single entry for user session

Whats happening :- I am using connect-mongo to store user session. As far as I read, we can store multiple user session in db as long as server is not restarted(?). I have a login page and whenever user logs in I store email address in session. I can see an entry created in mongodb. Server is still running and log-in with different credentials using incognito tab, I see the previous entry is deleted and replaced by new user. Hence at any time, there is just one recently logged in user in db.

What I want :- I want to store sessions for each user who has logged in. And when one logout, I check email address of log out request against db entries and delete that session. So my server.js contain this code :-

var cookieParser = require('cookie-parser');
var MongoStore = require('connect-mongo')(session);
app.use(cookieParser());
app.use(session({
    cookie: { maxAge: 1000*60*2 } ,
    secret: "session secret" ,
    store:new MongoStore({
        db: 'express',
        host: '127.0.0.1',
        port: 27017,  
        url:"mongodb://localhost:27017/db",
        collection: 'session', 
        auto_reconnect:true,
        resave: true,
        saveUninitialized: true
    })
 }));

apiRoutes.post('/login', function(req, res) {
  User.findOne({
    email: req.body.email
  }, function(err, user) {
    if(!err)
      req.session.email = req.body.email;
       return res.json({ success: true ,message:"Session saved",status:200});
       });
  });

apiRoutes.post('/logout',function(req,res){
mongoose.connection.db.collection('sessions').find({session.email:req.body.email}, function(err, data) {
        if(err){
        console.log("Error");
        }
        else{
          //delete entry
      }
   })
 });

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