Queue tree graph (SNMP/RRDtool)

Hi.
First of all sorry for my English.
I am creating a management software that monitors a router, I could create traffic graphs of the single queue consulting for SNMP and working with RRDTool, now I need also graphed some queue tree, making a print oid I see “bytes” but I do not understand whether incoming or outgoing.
In simple queues I work with IN and OUT and is working well. Could someone please clarify what are the values ​​to consult in the event queue tree. Greetings and thank you very much from now.