mat-tree will not horizontal scroll

[gubo]

Reproduction

https://github.com/gubo/tree-test.git

Expected Behavior

That <mat-tree ...> should horizontal scroll when a node extends the tree beyond the horizontal width of its parent div.

Actual Behavior

Does not horizontal scroll.

Angular CLI: 9.0.0-rc.8
Node: 12.13.0
OS: darwin x64

Angular: 9.0.0-rc.9
... animations, common, compiler, compiler-cli, core, forms
... language-service, platform-browser, platform-browser-dynamic
... router
Ivy Workspace: Yes

Package Version

@angular-devkit/architect 0.900.0-rc.8
@angular-devkit/build-angular 0.900.0-rc.8
@angular-devkit/build-optimizer 0.900.0-rc.8
@angular-devkit/build-webpack 0.900.0-rc.8
@angular-devkit/core 9.0.0-rc.8
@angular-devkit/schematics 9.0.0-rc.8
@angular/cdk 8.2.3
@angular/cli 9.0.0-rc.8
@angular/material 8.2.3
@ngtools/webpack 9.0.0-rc.8
@schematics/angular 9.0.0-rc.8
@schematics/update 0.900.0-rc.8
rxjs 6.5.4
typescript 3.6.4
webpack 4.41.2

chrome,safari,edge,firefox,opera
macOS

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