How can i group the list command using SPFx ListView Command Set extension via manifest file

How can i group the list command using SPFx ListView Command Set extension via manifest file for SharePoint Add-in? Attached the image how i want. Below is my manifest file

{
"$schema": "https://developer.microsoft.com/json-schemas/spfx/command-set-extension-manifest.schema.json",

"id": "e0947d89-adb7-48cc-bb9b-40a6a676b6d3",
"alias": "DocumentLibraryCommandSet",
"componentType": "Extension",
"extensionType": "ListViewCommandSet",

"version": "*",
"manifestVersion": 2,

"requiresCustomScript": false,

"items": {
"COMMAND_1": {
"title": { "default": "Command One" },
"iconImageUrl": "icons/request.png",
"type": "command",
"commandGroup": "CUSTOM_GROUP",
"children": [
{
"title": "Child Command 1",
"command": "COMMAND_CHILD_1"
},
{
"title": "Child Command 2",
"command": "COMMAND_CHILD_2"
}
]
},
"COMMAND_2": {
"title": { "default": "Command Two" },
"iconImageUrl": "icons/cancel.png",
"type": "command"
}
}
}