How to animate the next item smoothly when expanding the previous item in recyclerview

I'm making an expandable nested recyclerview.

I have implemented both a parent recycler view and a child(nested) recycler view, but I would like the next item to be pushed out more smoothly when the previous item is expanded.

I'll show you an example image.

First what I want.

But what I made.

If you look at the GIF file, you won't notice much of a difference.

However, in the app in the first picture I referenced, when the first item is expanded, the second item is pushed out really smoothly.

However, what I made is that when the first item is expanded, the second item is pushed out like a break.

How can I make it softly pushed out?

I implemented it in epoxy, but I don't think RecyclerView will be any different.

thank you.

ParentController

class ParentEpoxyController : EpoxyController() {
    private var data : List<ParentItem> = listOf()
            set(value) {
                field = value
                requestModelBuild()
            }

    override fun buildModels() {
        data.forEachIndexed { index, item ->
            ParentDataModel_()
                .id(index)
                .title(item.workout)
                .list(item.list)
                .onBind { model, holder, position ->

                    bindParentRV(holder,item)
                    bindNestedRV(holder,item)
                }
                .addTo(this)
        }
    }

    private fun bindParentRV(holder: ParentDataModel.ItemViewHolder, item: ParentItem) {
        holder.apply {
            expandBtn.setOnClickListener {
                nestedRV.isVisible = !item.isExpandable
                borderline.isVisible = !item.isExpandable
                item.isExpandable = !item.isExpandable
                requestModelBuild()
            }
        }
    }

    private fun bindNestedRV(holder: ParentDataModel.ItemViewHolder, item: ParentItem) {
        holder.nestedRV.apply {
            val controller = ChildEpoxyController()
            controller.setItem(item.list)
            adapter = controller.adapter
            isVisible = item.isExpandable
        }
    }

    fun setItem(items : List<ParentItem>) {
        data = items
    }
}