System Information
Operating system: Linux-4.19.30_1-x86_64-with-glibc2.9 64 Bits
Graphics card: TITAN X (Pascal)/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 418.43

Blender Version
Broken: version: 2.80 (sub 51), branch: master, commit date: 2019-03-26 18:57, hash: rB337eb8c1de4c
Worked: -

Short description of error
When using the old grouping shortcut (CTRL + G) on a few objects to create a collection with them in it, the collection is not visible in the Outliner, only in the Object Properties window.
The same thing happens when appending a particle system emitter and its instances that are in a collection. While the particle system works, the collection of instances only show that they're in a collection in the object properties, not in the outliner.
Ideally, any imported collections should also show up in the outliner.

Exact steps for others to reproduce the error

Method 01

• Create object
• Hit CTRL+G to add it to a collection
• Collection invisible in outliner

Method 02

• Create object with particle system
• Create set of particle instances
• Add particle instances to collection and set particles to render "Collection"
• Save file
• Append particle emitter and instances to new file
• Instance collection does not show up in outliner, only object properties