Nested CollectionView Cell did not appear - ios

Question

I nested collectionView inside collectionView Cell like this:
inside first collectionView Cell, I put this code :
class CaseCellView: UICollectionViewCell, UICollectionViewDelegate, UICollectionViewDataSource {
#IBOutlet weak var lblHeader: UILabel!
#IBOutlet weak var collectionViewItemList: UICollectionView!
var sellingArray = ["1", "2", "3", "4", "5"]
override func awakeFromNib(){
super.awakeFromNib()
let flowLayout = UICollectionViewFlowLayout()
flowLayout.scrollDirection = .horizontal
flowLayout.itemSize = CGSize(width: collectionViewItemList.frame.width, height: collectionViewItemList.frame.width)
flowLayout.minimumLineSpacing = 5.0
flowLayout.minimumInteritemSpacing = 5.0
self.collectionViewItemList.collectionViewLayout = flowLayout
self.collectionViewItemList?.delegate = self
self.collectionViewItemList?.dataSource = self
self.collectionViewItemList.reloadData()
}
func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
return self.sellingArray.count
}
func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAt indexPath: IndexPath) -> CGSize {
return CGSize(width: collectionViewItemList.frame.width, height: collectionViewItemList.frame.width)
}
func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, insetForSectionAt section: Int) -> UIEdgeInsets {
return UIEdgeInsetsMake(0, 0, 0, 0)
}
func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
let cell1 = collectionView.dequeueReusableCell(withReuseIdentifier: "caseListCell", for: indexPath)as! CaseListCellView
cell1.lblItemList.text = self.sellingArray[indexPath.item]
cell1.lblItemList.textColor = .white
cell1.backgroundColor = UIColor.blue
return cell1
}
}
class CaseListCellView: UICollectionViewCell {
#IBOutlet weak var lblItemList: UILabel!
override func awakeFromNib() {
super.awakeFromNib()
}
}
but when I run, the nested collectionView result did not appear inside the first collectionView, it just show first lblHeader from the first collectionView Cell.
How to correct my code to show nested collectionView Cell?