How can I get the coordinates of a node (JLabel,image, ..) on a JTree?

Use any one of the following methods to get rectangular bounds of a cell -

public Rectangle getRowBounds(int row)
Returns the Rectangle that the node at the specified row is drawn in.
Parameters:
row - the row to be drawn, where 0 is the first row in the display
Returns:
the Rectangle the node is drawn in

public Rectangle getPathBounds(TreePath path)
Returns the Rectangle that the specified node will be drawn into. Returns null if any component in the path is hidden (under a collapsed parent). 
Note:
This method returns a valid rectangle, even if the specified node is not currently displayed.

Parameters:
path - the TreePath identifying the node
Returns:
the Rectangle the node is drawn in, or null

rectangle.x and rectangle.y should give you the coordinates relative to the tree.