Shams,
1. Adding space between image and node.
2. Hiding + and - signs against expandable nodes.
These kinds of tasks can be performed by changing sizes of the images.
3. Add images to all nodes (which is easy via xml), but make them expand and collapse by clicking on those images.
Do you mean the same functionality as with plus/minus images? Probably this can be also implemented when you merge plus/minus icons with the node image.