How to do multi-level push of array element in mgo?

So I want to do a multi level push for the struct below :

type Inspector_Pool struct{
    Unique_Id string `json:"unique_id" form:"unique_id" query:"unique_id"`
    Email string `json:"email" form:"email" query:"email"`
    Branch []string `json:"branch" query:"branch"`
    Date []Date `json:"date" query:"date"`
}

type Date struct {
	Event_Timestamp string `json:"event_timestamp" query:"event_timestamp"`
	Event []Event `json:"event" query:"event"`
}

type Event struct {
	Event_Name string `json:"event_name" form:"event_name" query:"event_name"`
	Event_Id string `json:"event_id" form:"event_id" query:"event_id"`
	Status string `json:"status" query:"status"`
}

So what i want is to push data in Event array so what I have to achieve code below:

//push a new node in date array
query := bson.M{"branch":"400612", "unique_id":c.Unique_Id}
update := bson.M{"$push": bson.M{"date": bson.M{"event_timestamp": t, "event": []models.Event{
		{
			Event:models.INSPECTION,
			Event_Id:"123456789",
			Status:models.PENDING,
		},

}}}}

err = look_up.Update(query, update)
if err != nil {
	panic(err)
}

//push the data in the nested event 
pushQuery := bson.M{"date.event": bson.M{"event": []models.Event{
	{
		Event_Name:models.INSPECTION,
		Event_Id:"4984984198",
		Status:models.PENDING,
	},
}}}

err = look_up.Update(bson.M{"unique_id": "2549090", "date.event_timestamp":"08-05-2017"}, bson.M{"$push": pushQuery})
if err != nil {
	//panic(err)
	fmt.Print("error_2",err)
}

but it doesn'tpush it in the event object but instead create a new entry in date object heres the snapshot

You can utilise the $ positional operator to update. Which basically identifies an element in an array to update without explicitly specifying the position of the element in the array.

Alter your second push statement as below:

pushQuery := bson.M{"date.$.event": Event{    
        Event_Name:"foobar",
        Event_Id:"4984984198",   
}}
err = collection.Update(bson.M{"unique_id":"2549090", 
                               "date.event_timestamp":"08-05-2017"}, 
                        bson.M{"$push": pushQuery})

The above will push event 'foobar' into the same date array matching event_timestamp '08-05-2017' i.e.

{"_id": ObjectId("5909287934cb838fe8f89b6e"),
  "unique_id": "2549090",
  "date": [
    {
      "event_timestamp": "08-05-2017",
      "event": [
        {
          "event_name": "baz",
          "event_id": "123456789"
        },
        {
          "event_name": "foobar",
          "event_id": "4984984198"
        }
      ]
    }
  ]}

Generally having an array of array makes querying or extracting data difficult/complex later on. Depending on your application's use case, I would also suggest to re-consider your document Data Model.