code: func (h *Hasher) releaseTree() {
  	t := h.bmt
  	if t == nil {
  		return
  	}
  	h.bmt = nil
  	go func() {
  		t.cursor = 0
  		t.offset = 0
  		t.span = nil
  		t.section = make([]byte, h.pool.SegmentSize*2)
  		select {
  		case <-t.result:
  		default:
  		}
  		h.pool.release(t)
  	}()
  }
docs: // releaseTree gives back the Tree to the pool whereby it unlocks
  // it resets tree, segment and index