ttF = Tooltip[#, "The Iliad of Homer"] &;

Use `"The Iliad of Homer"` as the tooltip for the nodes and the edge:

    TreePlot[{ttF[# -> #2] & @@ ttF /@ {Peleus, Achiles}},  VertexLabeling -> All]

![enter image description here][1]


  [1]: https://i.sstatic.net/SANSj.gif