How to change the group icon in legend via Python in QGIS 2.6

Question

I would want that group created by plugin differs from the group created by man. ;) How to change the group icon in legend via Python in QGIS 2.6? At version 1.x I did it this way:

self.legendTree = self.iface.mainWindow().findChild(QDockWidget,"Legend").findChild(QTreeWidget)
currGrp=self.legendTree.currentItem()
currGrp.setIcon(0,self.setMyIcon("folder.png")

In pyqgis 2.6 I create group this way

root = QgsProject.instance().layerTreeRoot()
node_group1 = root.insertGroup(0, "Group 1")

But how to change the icon?