How to merge collections in Laravel 5?

Hello. Probably already balls for rollers came can't think how to drain the collection. In the foreach enumerates the users who have taken certain objects using hasMany. Get a list of collections (from 2 users):

Collection {#683 ▼
 #items: array:1 [▼
 0 => PitSold {#693 ▶}
]
}
Collection {#699 ▼
 #items: array:3 [▼
 0 => PitSold {#700 ▶}
 1 => PitSold {#704 ▶}
 2 => PitSold {#705 ▶}
]
}

How may I obtain a single collection with all elements:

Collection {#699 ▼
 #items: array:4 [▼
 0 => PitSold {#693 ▶}
 1 => PitSold {#700 ▶}
 2 => PitSold {#704 ▶}
 3 => PitSold {#705 ▶}
]
}