title: How to update my mat-tree without it rerendering?
body: <p>My mat tree redraws initializes itself on datasource data change using a BehaviorSubject.</p>
  
  <p>I am using an observable that i update form time to time in order to update the tree data generated by a FlatTreeControl.</p>
  
  <p>The code is pretty basic and easy to understand so I don't see the issue.</p>
  
  <p>I tried using a simplified version of the angular flat tree example on stackBlitz:
  <a href="https://stackblitz.com/angular/rlqvokgplrko?file=app%2Ftree-checklist-example.ts" rel="noreferrer">https://stackblitz.com/angular/rlqvokgplrko?file=app%2Ftree-checklist-example.ts</a></p>
  
  <p>Here is my version:
  <a href="https://stackblitz.com/edit/create-iq2meg" rel="noreferrer">https://stackblitz.com/edit/create-iq2meg</a></p>
  
  <p>What i expect is that as in the official mat-tree example, the data is updated dynamically WITHOUT having to redraw the entire tree and having it collapse on me each time.</p>