The 'onDragOver' event is available from
http://www.jeasyui.com/easyui/plugins/jquery.tree.js. Some codes looks like this:
$('#tt').tree({
dnd: true,
onDragOver: function(target, source){
var cc = $(this).tree('getChildren',target);
for(var i=0; i<cc.length; i++){
if (cc[i].target == source.target){return false} // return false to deny drop, restrict the node to move away from it parent
}
}
});