diff --git a/packages/application/src/shell.ts b/packages/application/src/shell.ts
index 3ece75171c..c6a230e96c 100644
--- a/packages/application/src/shell.ts
+++ b/packages/application/src/shell.ts
@@ -13,7 +13,7 @@ import { Message, MessageLoop, IMessageHandler } from '@lumino/messaging';
 
 import { ISignal, Signal } from '@lumino/signaling';
 
-import { Panel, Widget, BoxLayout } from '@lumino/widgets';
+import { Panel, Widget, BoxLayout, TabPanel } from '@lumino/widgets';
 
 /**
  * The Jupyter Notebook application shell token.
@@ -73,6 +73,7 @@ export class NotebookShell extends Widget implements JupyterFrontEnd.IShell {
     rootLayout.addWidget(this._main);
 
     this.layout = rootLayout;
+    this._mainIsTabPanel = false;
   }
 
   /**
@@ -103,12 +104,29 @@ export class NotebookShell extends Widget implements JupyterFrontEnd.IShell {
     return this._menuWrapper;
   }
 
+  /**
+   * Get the status of main area.
+   */
+  get mainIsTabPanel(): Boolean {
+    return this._mainIsTabPanel;
+  }
+
+  /**
+   * Set the status of main area.
+   */
+  set mainIsTabPanel(value: Boolean) {
+    this._mainIsTabPanel = value;
+  }
+
   /**
    * Activate a widget in its area.
    */
   activateById(id: string): void {
     const widget = find(this.widgets('main'), w => w.id === id);
     if (widget) {
+      if (this._mainIsTabPanel) {
+        (this._main.widgets[0] as TabPanel).tabBar.currentTitle = widget.title;
+      }
       widget.activate();
     }
   }
@@ -137,11 +155,16 @@ export class NotebookShell extends Widget implements JupyterFrontEnd.IShell {
       return this._menuHandler.addWidget(widget, rank);
     }
     if (area === 'main' || area === undefined) {
-      if (this._main.widgets.length > 0) {
+      let main = this._main;
+
+      // If main area is a TabPanel, then the widget is added to it.
+      if (this._mainIsTabPanel) main = main.widgets[0] as TabPanel;
+      else if (this._main.widgets.length > 0) {
         // do not add the widget if there is already one
         return;
       }
-      this._main.addWidget(widget);
+
+      main.addWidget(widget);
       this._main.update();
       this._currentChanged.emit(void 0);
     }
@@ -175,7 +198,10 @@ export class NotebookShell extends Widget implements JupyterFrontEnd.IShell {
       case 'menu':
         return iter(this._menuHandler.panel.widgets);
       case 'main':
-        return iter(this._main.widgets);
+        // If the main area is a TabPanel returns the list of its Widgets.
+        if (this._mainIsTabPanel)
+          return iter((this._main.widgets[0] as TabPanel).widgets);
+        else return iter(this._main.widgets);
       default:
         throw new Error(`Invalid area: ${area}`);
     }
@@ -188,6 +214,7 @@ export class NotebookShell extends Widget implements JupyterFrontEnd.IShell {
   private _spacer: Widget;
   private _main: Panel;
   private _currentChanged = new Signal<this, void>(this);
+  private _mainIsTabPanel: Boolean;
 }
 
 /**
diff --git a/packages/tree-extension/src/index.ts b/packages/tree-extension/src/index.ts
index 5fb709e4fc..38f69f054e 100644
--- a/packages/tree-extension/src/index.ts
+++ b/packages/tree-extension/src/index.ts
@@ -31,6 +31,7 @@ import {
 } from '@jupyterlab/ui-components';
 
 import { Menu, MenuBar, TabPanel } from '@lumino/widgets';
+import { NotebookShell } from '@jupyter-notebook/application';
 
 /**
  * The file browser factory.
@@ -116,6 +117,11 @@ const browserWidget: JupyterFrontEndPlugin<void> = {
     const tabPanel = new TabPanel({ tabPlacement: 'top', tabsMovable: true });
     tabPanel.addClass('jp-TreePanel');
 
+    // Add the TabPanel to the main area.
+    app.shell.add(tabPanel, 'main', { rank: 100 });
+    // Set the main area as a TabPanel.
+    (app.shell as NotebookShell).mainIsTabPanel = true;
+
     const trans = translator.load('notebook');
 
     const { defaultBrowser: browser } = factory;
@@ -124,8 +130,7 @@ const browserWidget: JupyterFrontEndPlugin<void> = {
     browser.node.setAttribute('aria-label', trans.__('File Browser Section'));
     browser.title.icon = folderIcon;
 
-    tabPanel.addWidget(browser);
-    tabPanel.tabBar.addTab(browser.title);
+    app.shell.add(browser, 'main');
 
     // Toolbar
     toolbarRegistry.addFactory(
@@ -155,8 +160,7 @@ const browserWidget: JupyterFrontEndPlugin<void> = {
       running.id = 'jp-running-sessions';
       running.title.label = trans.__('Running');
       running.title.icon = runningIcon;
-      tabPanel.addWidget(running);
-      tabPanel.tabBar.addTab(running.title);
+      app.shell.add(running, 'main');
     }
 
     // show checkboxes by default if there is no user setting override
@@ -171,8 +175,6 @@ const browserWidget: JupyterFrontEndPlugin<void> = {
       .catch((reason: Error) => {
         console.error(reason.message);
       });
-
-    app.shell.add(tabPanel, 'main', { rank: 100 });
   }
 };