In Particle System, Create and assign a Particle System as Sub Emitter. now create its preset. On clicking Sub Emitter Property in preset, Editor goes into the not-responding state. need to manually kill the Unity editor.
refer attached video

Steps to repro:
1. Create a new project
2. Hierarchy > right-click > Effects > Particle System
3. Inspector > Particle System > Enable Sub Emitters
4. Sub Emitters > Create and assign a Particle System as Sub Emitter
5. Inspector > Particle System > Create Preset
6. Inspector > Preset > (Click On)Sub Emitter

Actual Result:
Editor freezes when Sub Emitter option is clicked from Particle System preset

Expected Result:
Inside particle system preset on clicking sub emitter option, it should load gracefully

Reproducible in:
2020.2.0a20

Working Fine in:
2020.2.0a19, 2020.1.1f1, 2019.4.6f1.

Environment:
Windows 10 and macOS 10.15