The checked status about node's checkbox or radio when zTree was initialized. It is valid when [setting.check.enable = true & treeNode.nocheck = false]
1. Do not initialize it, it will be initialized when the node is initialized.
2. If you need to achieve special features, you can use the zTreeObj.getChangeCheckedNodes method and modify the value of 'checkedOld' attribute.
Default: the value of 'checked' attribute when zTree is initialized
true means: the checkbox or radio is checked when zTree is initialized.
false means: the checkbox or radio is not checked when zTree is initialized.
var treeObj = $.fn.zTree.getZTreeObj("tree");
var checkedOld = treeObj.getNodes()[0].checkedOld;