fixed mat-tree not closing children in tree-dynamic-example file as well

Author: Victoria Wei

src/material-examples/tree-dynamic/tree-dynamic-example.ts

@@ -94,13 +94,22 @@ export class DynamicDataSource {
 
     node.isLoading = true;
 
+    let count = 0;
+
     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);
+        for (let i = index + 1; i < this.data.length; i++) {
+          if (this.data[i].level > node.level) {
+            count++;
+          } else {
+            break;
+          }
+        }
+        this.data.splice(index + 1, count);
       }
 
       // notify the change