Finally! After 3 painful days of creating a hierarchy tree using Oracle ADF tree component, I DID IT!!
It’s all about creating a different View Object (VO) for the top/root level and another VO for the other levels. Then creating a View Link (VL) from the top level VO to the normal VO with a 1-many relationship; and another VL from the normal VO back to itself with also a 1-to-many relationship
Following up to this, now I need to find out how to add a link or something to the last level so that upon clicking on the node will display its specified panel.
* I will document this, someday!