docs(tree): add more tree demos

[tinayuangao]

No description provided.

[jelbourn]

LGTM

[jesben]

Thanks for the demos.

I'm trying to implement asynchronous data retrieval with http service, I can not make it work. Sub nodes are not added on first click, visible after second click! Please help?

Added setTimeout for illustration

dynamic-database.ts

toggleNode(node: DynamicFlatNode, expand: boolean) {
    const children = this.database.getChildren(node.item);
    const index = this.data.indexOf(node);
    if (!children || index < 0) { // If no children, or cannot find the node, no op
      return;
    }

    // Doesn't work
    setTimeout(() => {
      if (expand) {
        const nodes = children.map(name =>
            new DynamicFlatNode(name, node.level + 1, this.database.isExpandable(name)));
        this.data.splice(index + 1, 0, ...nodes);
      } else {
        this.data.splice(index + 1, children.length);
      }

      // notify the change
      this.dataChange.next(this.data);
    }, 0);
  }

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