How to reproduce:
1. Open the "Tree_Crash.zip" project
2. Open the "Scene.unity" scene
3. Open the "Tree" prefab
4. Enter Play Mode
5. Switch to Scene View
6. Exit Play Mode
7. Exit Prefab View
8. Enter Play Mode

Actual result: Unity crashes.

Reproducible with: 2018.3.0a6, 2018.4.5f1, 2019.1.12f1, 2019.2.0b10, 2019.3.0a10.

Notes:
A failed assertion is thrown when entering Play mode in prefab mode:
Assertion failed on expression: 'm_TreeNode.IsInList()'

Failed Assertions starts spamming after leaving Play Mode in prefab mode with Scene View opened:
Assertion failed on expression: 's_VisibleTreeNodes.empty()'
UnityEngine.GUIUtility:ProcessEvent(Int32, IntPtr)

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Fixed in 2020.1.0a20, 2019.3.0f6.