nested objects insert

var eventSystem = require ("mongoose");
eventSystem.connect('mongodb://localhost/historydb', { useNewUrlParser: true });
var linkPostSchema= new eventSystem.Schema({
    linkurl: String,
    title: String,
    story: String
});
var linkPost = eventSystem.model("linkPost", linkPostSchema);
var imagePostSchema= new eventSystem.Schema({
    src: String,
    title: String,
    story: String
});
var imagePost = eventSystem.model("imagePost", imagePostSchema);
var postSchema= new eventSystem.Schema({
    link: [linkPostSchema],
    image: [imagePostSchema]
});
var Post = eventSystem.model("Post", postSchema);
var eventSchema = new eventSystem.Schema({
    name: String,
    date: Date,
    story: String,
    posts: [postSchema]
});

var Event = eventSystem.model("Event", eventSchema);
var newEvent = new Event({
    name: "MAIN EVENT",
    date: Date.now(),
    story: "main event story"
});

newEvent.posts.push(
     {
         imagePost: {
             src: "first.jpg",
             title: "image post title",
             story: "image post story"
        },
        linkPost: {
            linkurl: "https://youtube.com",
            title: "link post title",
            story: "link post story"
        }
    });
newEvent.save(function(err, event){
    if (err){
        console.log(err);
    }else {
console.log(event);
    }
});