How To push dynamic formGroup in Dynamic Created Form Array

Actually am trying to apply reactive forms approach in my project here in my project i have to add a Add Season Button and when button is clicked then a new formGroup is added with one form Control i.e season and one FormArray i.e episodes so that means episodes is created Dynamically now i want to add some more formGroup in episodes but am unable to figure out how to do that here what i have done so far:

export class AddContentsComponent implements OnInit, AfterViewChecked {
  count = 0
  episodes = []
  ContentForm: FormGroup
  constructor() { }

  ngOnInit() {
    this.ContentForm = new FormGroup({
      'title': new FormControl(null, Validators.required),
      'desc': new FormControl(null, Validators.required),
      'image_url': new FormControl(null, Validators.required),
      'subtitle_url': new FormControl(null, Validators.required),
      'url': new FormControl(null, Validators.required),
      'episodes': new FormArray([]),
      'seasons': new FormArray([])
    })
  }

 onSubmit() {
    console.log(this.ContentForm)
  }
addSeasons() {
while ((<FormArray>this.ContentForm.get('episodes')).length) {
      console.log('ok');
      (<FormArray>this.ContentForm.get('episodes')).removeAt((<FormArray>this.ContentForm.get('episodes')).length - 1);
    }

    (this.ContentForm.get('seasons') as any).push(new FormGroup({
      'season': new FormControl(null),
      'episodes': new FormArray([]) //here am add a dynamic formArray
    }))
  }


  DeleteSeason(index) {
    (<FormArray>this.ContentForm.get('seasons')).removeAt(index)
  }



  AddEpisodesInSeasons(index) {
    (<FormArray>this.ContentForm.get('seasons')) //now here i want to push new FormGroup to **episodes**
  }

}

https://stackblitz.com/edit/angular-ndnstv for more..