Get the node's index in the same level nodes. (start from 0)
Please use zTree object to executing the method.
JSON data object of the node which need to get index.
Please ensure that this data object is an internal node data object in zTree.
return the index. (start from 0)
If there is no this node, return -1.
var treeObj = $.fn.zTree.getZTreeObj("tree");
var nodes = treeObj.getSelectedNodes();
if (nodes.length>0) {
var index = treeObj.getNodeIndex(nodes[0]);
}