How can I nest entire event inside a single json field while remapping in vrl?

[sainad2222]

Before:

{
"field1": "val1",
"field2": "val2"
}

After:

{
  "event": {
  "field1": "val1",
  "field2": "val2"
  },
 "event_type": "type1"
}

I tried this but doesn't seem to work as expected

transforms:
  restructure_event:
    type: "remap"
    inputs:
      - "input1"
    source: |
      .event = .
      .event_type = "type1"

Edit:
After trying this

.event = merge({}, .)
.event_type = "type1"

I am able to nest but need a way to delete all fields except "event" and "event_type"
TIA

[sainad2222]

.event, _err = merge({}, .)
template = {}
template.event = .event
. = template
.source_type = "prometheus"

Thanks to britton on discord