public <T>void insert(List<T> list,T object,int position){
  list.add(position,object);
  if (customHeaderView != null)   position++;
  notifyItemInserted(position);
}

public < T > void insert ( List < T > list , T object , int position ) { list . add ( position , object ) ; if ( customHeaderView != null ) position ++ ; notifyItemInserted ( position ) ; }
insert a item to the list of the adapter
