You must create Panel in order to control the order.
map.createPane('myPane1'); map.createPane('myPane2'); map.getPane('myPane1').style.zIndex = 400; map.getPane('myPane2').style.zIndex = 800;
map.createPane('myPane1');
map.createPane('myPane2');
map.getPane('myPane1').style.zIndex = 400;
map.getPane('myPane2').style.zIndex = 800;
With this you can add the layer to the pane you want.