BlendTree overlaps and hides another Blendtree on adding the Motion Field. Unable to select other Blend Tree once it is hidden.

Steps to repro:
1. Open the attached Project.
2. Open the TestAnimator Controller > Double click on "Blend Tree".
3. Right Click on Blend Tree node > Add two Blend Tree.
4. Select first Blend Tree and add 6-7 Motion Field from the Inspector.

Actual Result:
BlendTree overlaps and hides another Blendtree.

Expected Result:
Blend Tree should not be overlapped and maintain visibility.

Reproducible on:
2020.1.0a10, 2019.3.0b8, 2019.2.01f1, 2019.1.0f1, 2017.1.5f1.

Environment:
Windows 10 & Mac 10.14.