How to append an array in GROQ?

[...a, ...b]

"items": [
  *[_type == "groupsPage"][0] {
    "title": "Overview",
    "url": "/aag-ugsg/"
  },
  ...(*[_type == "groupsPages"] {
    title,
    "url": "/aag-ugsg/" + slug.current
  })
]