Firebase - How to sort the data by newly added child (Swift)?

Question

let childRef = ref.child("Order")
    childRef.observeEventType(.Value, withBlock: {(snapshot : FIRDataSnapshot) in
       self.count = snapshot.childrenCount
        self.something = snapshot.value as! NSDictionary
        self.keys = self.something.allKeys as! [String]
        print(self.keys)
        self.ordersTable.reloadData()
    })

Here, I'm able to retrieve all the data under "Order". But I'm getting the older data first and latest data in the last. But I want the newly added data first. Could anyone please let me know how to do it? My structured data is shown below. Under every childByAutoID(-KLIXR0Al_vJKixcuG7K) I have around 10 more child.