The tree already had a parent, the scroll pane's view port (which has the scroll pane as its parent). When you try to add it to a new parent, things go wrong. Instead of adding the tree itself again, you should add the scroll pane, which contains the tree.
You should also ignore the bounds and visibility. The parent panel (PanelResourceWindow) will take care of the bounds of the scroll pane through its layout manager. The visibility will be set as the parent PanelResourceWindow becomes visible or invisible.