What does "arg tree" mean?

Hi experts,
I met with one function in RooAbsArg class:
RooArgSet* getObservables(const RooAbsData* data) const
The documentation explains:
Create a list of leaf nodes in the arg tree starting with
ourself as top node that match any of the names of the variable list
of the supplied data set (the dependents).
I guess this “arg tree” is a series a args. They’re organized as a tree? What does “starting with ourself as top node” mean?
Thank you very much.