private void checkMouseEvent(MouseEvent e) {
		int selectedRow = tree.getRowForLocation(e.getX(), e.getY());

		if (selectedRow < 0) {
			return;
		}

		if (e.getClickCount() == 2 && e.getButton() == MouseEvent.BUTTON1) {
			TreePath path = tree.getPathForRow(selectedRow);
			ProgramNode node = (ProgramNode) path.getLastPathComponent();
			plugin.doubleClick(node);
		}
	}
Set the action state depending on what the user double-clicked. 

Row = -1: The user clicked the expand/collapse icon.  Just nothing regarding
          selection or the view.
Row = 0+: The user clicked a node (root or fragment); select that node
          for view.
Ghidra/Features/Base/src/main/java/ghidra/app/plugin/core/programtree/ProgramTreePanel.java