code: func (blink *blink) Insert(keys ...Key) Keys {
  	if len(keys) > numberOfItemsBeforeMultithread {
  		return blink.multithreadedInsert(keys)
  	}
  	overwritten := make(Keys, 0, len(keys))
  	stack := make(nodes, 0, blink.ary)
  	for _, k := range keys {
  		overwritten = append(overwritten, blink.insert(k, &stack))
  		stack.reset()
  	}
  
  	return overwritten
  }
docs: // Insert will insert the provided keys into the b-tree and return
  // a list of keys overwritten, if any.  Each insert is an O(log n)
  // operation.