CheckBox ButtonGroup The third level is not fully selected, the first level is not half selected

import QtQuick 2.12
import QtQuick.Controls 2.12
import QtQuick.Layouts 1.12

ListView{
    id: listView
    clip: true
    property var  childGroup
    Layout.fillHeight: true
    ScrollBar.vertical: ScrollBar { }

}

import QtQuick 2.12
import QtQuick.Controls 2.12
import QtQuick.Layouts 1.12

Rectangle {
    id: itemTree
    width: 1920
    height: 1440
    property var checkedArray: [] //当前已勾选的items
    property int spacing: 10    //项之间距离
    property int indent: 5      //子项缩进距离,注意实际还有icon的距离
    property int  itemHeight: 50

    Component{
        id: delegateComponent
        ItemDelegate{
                   id: delegate
                   width: listView.width
                   checkable: true

                   contentItem: ColumnLayout {
                       spacing: 10

                       ButtonGroup {
                           id: parentChildGroup
                           exclusive: false
                           checkState:  parentBox.checkState
                       }


                       CheckBox {
                           id: parentBox
                           text: modelData.className
                           font.bold: true
                           //elide: Text.ElideRight
                           //Layout.fillWidth: true
                           Layout.preferredWidth: 200
                           checkState: parentChildGroup.checkState
                           ButtonGroup.group:  delegate.parent.parent.childGroup ?
                                                    delegate.parent.parent.childGroup : null
                       }

                       ColumnLayout {
                           id: grid
                           visible: false
                           Layout.fillHeight: true
                           Layout.preferredHeight: childTree.contentHeight//  (itemHeight + 10) * modelData.subnodes.length
                           BambooTreeListView {
                               id: childTree
                               height: itemHeight
                               model: modelData.subnodes
                               delegate: delegateComponent
                               Layout.fillWidth: true
                               Layout.fillHeight: true
                               childGroup: parentChildGroup
                           }

                       }
                   }

                   states: [
                       State {
                           name: "expanded"
                           when: delegate.checked

                           PropertyChanges {
                               target: grid
                               visible: true
                           }
                       }
                   ]
               }
    }



   BambooTreeListView{
       id: listView
       anchors.fill: parent
       delegate: delegateComponent
       ScrollBar.vertical: ScrollBar { }
   }



    Component.onCompleted: {
        setTestDataB();
    }


    function setTestDataB(){
        listView.model=JSON.parse('[
        {
            "className":"1 one",
            "istitle":true,
            "subnodes":[
                {
                    "className":"1-1",
                    "istitle":true,
                    "subnodes":[
                        {"className":"1-1-1","isoption":true, "subnodes":[]},
                        {"className":"1-1-2","isoption":true, "subnodes":[]}
                    ]
                },
                {
                    "className":"1-2",
                    "istitle":true,
                    "subnodes":[
                        {"className":"1-2-1","isoption":true, "subnodes":[]},
                        {"className":"1-2-2","isoption":true, "subnodes":[]}
                    ]
                }
            ]
        },
        {
            "className":"2 one",
            "istitle":true,
            "subnodes":[
                {"className":"2-1","istitle":true, "subnodes":[]},
                {
                    "className":"2-2",
                    "istitle":true,
                    "subnodes":[
                        {"className":"2-2-1","isoption":true, "subnodes":[]},
                        {"className":"2-2-2","isoption":true, "subnodes":[]}
                    ]
                }
            ]
        },
        {"className":"3 one","istitle":true, "subnodes":[]},
        {
            "className":"4 one",
            "istitle":true,
            "subnodes":[
                {"className":"4-1","istitle":true, "subnodes":[]},
                {"className":"4-2","istitle":true, "subnodes":[]}
            ]
        }
    ]')
    }
}