ListView displays weird spaces when adding elements in delegate's onCompleted callback

import QtQuick 2.9
import QtQuick.Window 2.2

Window {
    width: 640
    height: 480
    visible: true

    ListModel {
        id: listModel
        ListElement { name: "a" }
        ListElement { name: "b" }
        ListElement { name: "c" }
        ListElement { name: "d" }
        ListElement { name: "e" }
        ListElement { name: "f" }
        ListElement { name: "g" }
        ListElement { name: "h" }
        ListElement { name: "i" }
        ListElement { name: "j" }
    }

    ListView {
        id: treeView
        anchors.fill: parent
        model: listModel

        delegate: Text {
            text: name
            Component.onCompleted: {
                console.log(index, name);
                if (name.length === 1) {
                    for (var i = 0; i < 10; ++i)
                        listModel.insert(index + 1, {name: name + i});
                }
            }
        }
    }
}