fix keyboarding behavior for right and left arrow keys in Tree View

change/@microsoft-fast-foundation-ee6e3feb-c675-4e87-988c-c2fcdc71f6f6.json

@@ -0,0 +1,7 @@
+{
+  "type": "patch",
+  "comment": "fix keyboarding behavior for right and left arrow keys in Tree View",
+  "packageName": "@microsoft/fast-foundation",
+  "email": "chhol@microsoft.com",
+  "dependentChangeType": "patch"
+}

packages/web-components/fast-foundation/src/tree-view/tree-view.ts

@@ -147,16 +147,32 @@ export class TreeView extends FoundationElement {
             case keyArrowLeft:
                 if (e.target && this.isFocusableElement(e.target as HTMLElement)) {
                     const item = e.target as HTMLElement;
-                    if (item instanceof TreeItem && item.childItemLength() > 0) {
+
+                    if (
+                        item instanceof TreeItem &&
+                        item.childItemLength() > 0 &&
+                        item.expanded
+                    ) {
                         item.expanded = false;
+                    } else if (
+                        item instanceof TreeItem &&
+                        item.parentElement instanceof TreeItem
+                    ) {
+                        TreeItem.focusItem(item.parentElement);
                     }
                 }
                 return false;
             case keyArrowRight:
                 if (e.target && this.isFocusableElement(e.target as HTMLElement)) {
                     const item = e.target as HTMLElement;
-                    if (item instanceof TreeItem && item.childItemLength() > 0) {
+                    if (
+                        item instanceof TreeItem &&
+                        item.childItemLength() > 0 &&
+                        !item.expanded
+                    ) {
                         item.expanded = true;
+                    } else if (item instanceof TreeItem && item.childItemLength() > 0) {
+                        this.focusNextNode(1, e.target as TreeItem);
                     }
                 }
                 return;