code: public boolean put(ExpirableReference expirable)
      {
          if (TraceComponent.isAnyTracingEnabled() && tc.isEntryEnabled()) SibTr.entry(this, tc, "put", "ObjId=" + expirable.getID() + " ET=" + expirable.getExpiryTime());
  
          boolean reply = tree.insert(expirable);
          if (reply)
          {
              size++;
          }
  
          if (TraceComponent.isAnyTracingEnabled() && tc.isEntryEnabled()) SibTr.exit(this, tc, "put", "reply=" + reply);
          return reply;
      }
docs: Add an ExpirableReference to the expiry index.
  @param expirable an ExpirableReference.
  @return true if the object was added to the index successfully.