If I Add the item on the recyclerview the item add duplicate

First time, If I add the item(click the send button) on the recyclerview, it does successfully,

but if I add the item second time, I expect see the item 1,2 but 1,2,1,2 add to the recyclerview

I'm using the multiViewType RecyclerView and the viewmodel

and I also use the databinding on the adapter code

Thank you for your help

below it's my code

private val commentList = mutableListOf<Comment>()
private var chatAdpater = ChatAdapter()
....

binding.sendBtn.setOnClickListener {
                postChat()
            }

.....

private fun postChat(){
    chatViewModel.postReChatResponse.observe(viewLifecycleOwner) {

        val newCommentList = mutableListOf<Comment>()
        commentList.add(
              Comment(
                nickname,
                description,
                writeTime,
                boardId.toInt(),
                categoryId.toInt(),
                id,
                images,
                2,
                commentsid.toInt(),
                0,
                null
               )
              )

         newCommentList.addAll(commentList)
         chatAdpater.setData(newCommentList,commentList.size-1)
   }
}


---------adapter-------

.....

var commentList:MutableList<Comment>? = mutableListOf()

.....

@SuppressLint("NotifyDataSetChanged")
    fun setData(commentList: MutableList<Comment>,position: Int){
        this.commentList = commentList
        notifyItemInserted(position)
    }

class ViewHolder(val binding: ChatItemListBinding) :
        RecyclerView.ViewHolder(binding.root) {
        fun onBind(data: Comment) {
            binding.comment = data
        }
    }

    class ReViewHolder(val bindingTwo: ReChatItemListBinding) :
        RecyclerView.ViewHolder(bindingTwo.root) {
        fun onBind(data: Comment) {
            bindingTwo.reComment = data
        }
    }

    override fun getItemViewType(position: Int): Int {
        return when (commentList!![position].isrecomment) {
            1 -> 1
            else -> 2
        }
    }

    override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): RecyclerView.ViewHolder {
        val binding =
            ChatItemListBinding.inflate(LayoutInflater.from(parent.context), parent, false)
        val bindingRe =
            ReChatItemListBinding.inflate(LayoutInflater.from(parent.context), parent, false)
        return when (viewType) {
            1 -> ReViewHolder(bindingRe)
            else -> ViewHolder(binding)
        }
    }

    override fun getItemCount(): Int{
        return commentList?.size ?: 0
    }

    override fun onBindViewHolder(holder: RecyclerView.ViewHolder, position: Int) {
        when (commentList?.get(position)?.isrecomment) {
            1 -> (holder as ReViewHolder).apply {
                holder.onBind(commentList!![position])
                 }
            2 -> (holder as ViewHolder).apply {
                holder.onBind(commentList!![position])
                holder.binding.chatText.setOnClickListener {
       
                 }
              }
           }