diff --git a/src/vs/base/common/map.ts b/src/vs/base/common/map.ts
index 45b81888e0a..560103a08c6 100644
--- a/src/vs/base/common/map.ts
+++ b/src/vs/base/common/map.ts
@@ -235,11 +235,11 @@ export class TrieMap<E> {
 
 	static PathSplitter = (s: string) => s.split(/[\\/]/).filter(s => !!s);
 
-	private _splitter: (s: string) => string[];
+	private readonly _splitter: (s: string) => string[];
 	private _root = new Node<E>();
 
 	constructor(splitter: (s: string) => string[]) {
-		this._splitter = splitter;
+		this._splitter = s => splitter(s).filter(s => Boolean(s));
 	}
 
 	insert(path: string, element: E): void {
@@ -695,4 +695,4 @@ export class LinkedMap<K, V> {
 			this._tail = item;
 		}
 	}
-}
\ No newline at end of file
+}
diff --git a/src/vs/platform/workspace/common/workspace.ts b/src/vs/platform/workspace/common/workspace.ts
index 2a922761192..f8ce46ebe97 100644
--- a/src/vs/platform/workspace/common/workspace.ts
+++ b/src/vs/platform/workspace/common/workspace.ts
@@ -131,7 +131,7 @@ export class LegacyWorkspace implements ILegacyWorkspace {
 
 export class Workspace implements IWorkspace {
 
-	protected _rootsMap: TrieMap<URI> = new TrieMap<URI>(TrieMap.PathSplitter);
+	private _rootsMap: TrieMap<URI> = new TrieMap<URI>(TrieMap.PathSplitter);
 
 	constructor(
 		public readonly id: string,
diff --git a/src/vs/workbench/api/node/extHostWorkspace.ts b/src/vs/workbench/api/node/extHostWorkspace.ts
index 2ef49280a8e..f42eb06cfa5 100644
--- a/src/vs/workbench/api/node/extHostWorkspace.ts
+++ b/src/vs/workbench/api/node/extHostWorkspace.ts
@@ -17,6 +17,7 @@ import { fromRange, EndOfLine } from 'vs/workbench/api/node/extHostTypeConverter
 import { IWorkspaceData, ExtHostWorkspaceShape, MainContext, MainThreadWorkspaceShape } from './extHost.protocol';
 import * as vscode from 'vscode';
 import { compare } from 'vs/base/common/strings';
+import { TrieMap } from 'vs/base/common/map';
 
 class Workspace2 extends Workspace {
 
@@ -24,29 +25,42 @@ class Workspace2 extends Workspace {
 		return data ? new Workspace2(data) : null;
 	}
 
-	private readonly _folder = new Map<URI, vscode.WorkspaceFolder>();
+	private readonly _folder: vscode.WorkspaceFolder[] = [];
+	private readonly _structure = new TrieMap<vscode.WorkspaceFolder>(s => s.split('/'));
 
 	private constructor(data: IWorkspaceData) {
 		super(data.id, data.name, data.roots);
 
+		// setup the workspace folder data structure
 		this.roots.forEach((uri, index) => {
-			this._folder.set(uri, {
+			const folder = {
 				name: basename(uri.fsPath),
 				uri,
 				index
-			});
+			};
+			this._folder.push(folder);
+			this._structure.insert(folder.uri.toString(), folder);
 		});
 	}
 
 	get folders(): vscode.WorkspaceFolder[] {
-		const ret: vscode.WorkspaceFolder[] = [];
-		this._folder.forEach(value => ret.push(value));
-		return ret;
+		return this._folder.slice(0);
 	}
 
 	getWorkspaceFolder(uri: URI): vscode.WorkspaceFolder {
-		let root = this._rootsMap.findSubstr(uri.fsPath);
-		return root && this._folder.get(root);
+		let str = uri.toString();
+		let folder = this._structure.lookUp(str);
+		if (folder) {
+			// `uri` is a workspace folder so we
+			let parts = str.split('/');
+			while (parts.length) {
+				if (parts.pop()) {
+					break;
+				}
+			}
+			str = parts.join('/');
+		}
+		return this._structure.findSubstr(str);
 	}
 }
 
diff --git a/src/vs/workbench/test/electron-browser/api/extHostWorkspace.test.ts b/src/vs/workbench/test/electron-browser/api/extHostWorkspace.test.ts
index c9a5e9cdd24..bd4c1109352 100644
--- a/src/vs/workbench/test/electron-browser/api/extHostWorkspace.test.ts
+++ b/src/vs/workbench/test/electron-browser/api/extHostWorkspace.test.ts
@@ -98,11 +98,14 @@ suite('ExtHostWorkspace', function () {
 		folder = ws.getWorkspaceFolder(URI.file('/Coding/Two/Nested/f'));
 		assert.equal(folder.name, 'Nested');
 
-		// folder = ws.getWorkspaceFolder(URI.file('/Coding/Two/Nested'));
-		// assert.equal(folder.name, 'Two');
+		folder = ws.getWorkspaceFolder(URI.file('/Coding/Two/Nested'));
+		assert.equal(folder.name, 'Two');
 
-		// folder = ws.getWorkspaceFolder(URI.file('/Coding/Two/Nested/'));
-		// assert.equal(folder.name, 'Two');
+		folder = ws.getWorkspaceFolder(URI.file('/Coding/Two/Nested/'));
+		assert.equal(folder.name, 'Two');
+
+		folder = ws.getWorkspaceFolder(URI.file('/Coding/Two'));
+		assert.equal(folder, undefined);
 	});
 
 	test('Multiroot change event should have a delta, #29641', function () {