class IntervalSkipList

def insert(range, marker)
  ranges[marker] = range
  first_node = insert_node(range.first)
  first_node.endpoint_of.push(marker)
  last_node = insert_node(range.last)
  last_node.endpoint_of.push(marker)
  cur_node = first_node
  cur_level = first_node.top_level
  while next_node_at_level_inside_range?(cur_node, cur_level, range)
    while can_ascend_from?(cur_node, cur_level) && next_node_at_level_inside_range?(cur_node, cur_level + 1, range)
      cur_level += 1
    end
    cur_node = mark_forward_path_at_level(cur_node, cur_level, marker)
  end
  while node_inside_range?(cur_node, range)
    while can_descend_from?(cur_level) && next_node_at_level_outside_range?(cur_node, cur_level, range)
      cur_level -= 1 
    end
    cur_node = mark_forward_path_at_level(cur_node, cur_level, marker)
  end
end