ztree樹(shù)中，一級(jí)節(jié)點(diǎn)圖標(biāo)如何顯示成文件夾

ztree樹(shù)中，如果一級(jí)節(jié)點(diǎn)沒(méi)有子節(jié)點(diǎn)，圖標(biāo)顯示成文件夾的形式，而不是文件的形式，該怎么設(shè)置？
我的setting是這樣設(shè)置的：

 setting: {
    data: {
        simpleData: {
            idKey: 'catId',
            pIdKey: 'parentId'
        },
        key: {
            name: 'catName',
            children: 'childCategories'
        }
    },
    check: {
        enable: true,
        chkboxType: {'Y': '', 'N': ''}
    }
}

樹(shù)節(jié)點(diǎn)mock數(shù)據(jù)：

 {
    "catId": 750620002,
    "catLevel": 1,
    "catName": "crossCateName1",
    "catNameEn": "crossCateNameEn1",
    "childCategories": [
        {
            "catId": 750620001,
            "catLevel": 2,
            "catName": "crossCateName2",
            "catNameEn": "crossCateNameEn2",
            "childCategories": [
                {
                    "catId": 750620000,
                    "catLevel": 3,
                    "catName": "crossCateName3",
                    "catNameEn": "crossCateNameEn3",
                    "parentId": 750620001,
                    "productPicType": 1,
                    "sortOrder": 1,
                    "status": 1
                }
            ],
            "parentId": 750620002,
            "sortOrder": 1,
            "status": 1
        }
    ],
    "parentId": 750620003,
    "sortOrder": 1,
    "status": 1
},
{
    "catId": 750611326,
    "catLevel": 1,
    "catName": "RanTest4",
    "catNameEn": "RanTest4IN",
    "sortOrder": 1,
    "status": 1
},
{
    "catId": 750611325,
    "catLevel": 1,
    "catName": "RanTest3",
    "catNameEn": "RanTest3",
    "sortOrder": 1,
    "status": 1
}