Laravel 5.5. - Create a Collection from two collections

I have two different collections from 2 eloquent requests ($training_sessions & $users_count)

My first collection is giving me information for training sessions :

2 => {#464 ▼
  +"date": "2018-02-24"
  +"id": 4
  +"debutsession": "13:30:00"
  +"finsession": "17:00:00"
  +"creneau": "13:30:00 - 17:00:00"
  +"created_at": null
  +"updated_at": null
  +"nom": "MYNAME"
  +"prenom": "MYSURNAME"
  +"salle": "ROOM NAME "
  +"sessions": "SESSION NAME"

And i have a second Collection which gives me a count of users that will participate to the session

0 => {#564 ▼
  +"id": 2
  +"userscount": 4
}
1 => {#562 ▼
  +"id": 3
  +"userscount": 1
}

I tried to find out which method would allow me to create a single collection which would give me for each training session the number of attendees i get from the second collection (field userscount)

For example for id = 2:

2 => {#464 ▼
  +"date": "2018-02-24"
  +"id": 2
  +"debutsession": "13:30:00"
  +"finsession": "17:00:00"
  +"creneau": "13:30:00 - 17:00:00"
  +"created_at": null
  +"updated_at": null
  +"nom": "MYNAME"
  +"prenom": "MYSURNAME"
  +"salle": "ROOM NAME "
  +"sessions": "SESSION NAME"
  +"userscount": 1
}

And for a session without any attendee i would have :

2 => {#464 ▼
  +"date": "2018-02-24"
  +"id": 2
  +"debutsession": "13:30:00"
  +"finsession": "17:00:00"
  +"creneau": "13:30:00 - 17:00:00"
  +"created_at": null
  +"updated_at": null
  +"nom": "MYNAME"
  +"prenom": "MYSURNAME"
  +"salle": "ROOM NAME "
  +"sessions": "SESSION NAME"
  +"userscount": 0
}

via Chebli Mohamed