diff --git a/README.md b/README.md
index bee99e3..f108dca 100644
--- a/README.md
+++ b/README.md
@@ -26,8 +26,9 @@ window.__glpythonMount = (args, send) => {
   const embedOrigin = "https://glpython-edu.github.io"
   const embedUrl = `${embedOrigin}/glpython-editor/index.html`
   const [sessionId, mode, ...optionArguments] = args
-  // Optional per block, separated by spaces in any order: "box" or
-  // "substitution" presets the visualizer's mode, and URLs of shared Python
+  // Optional per block, separated by spaces in any order: "box",
+  // "substitution" or "tree" presets the visualizer's mode ("tree" only with
+  // the feature "tree"), and URLs of shared Python
   // files to load as libraries, e.g. @GLPython.eval(box https://…/parser.py).
   // LiaScript splits macro arguments at commas, so "features=run,repl" arrives
   // as several arguments: they are joined back together here. Arguments that
@@ -37,17 +38,17 @@ window.__glpythonMount = (args, send) => {
     .join(",")
     .split(/\s+/)
     .filter(Boolean)
-  const visualizerMode = options.find((option) => option === "box" || option === "substitution") ?? null
+  const visualizerMode = options.find((option) => option === "box" || option === "substitution" || option === "tree") ?? null
   const libraryUrls = options.filter((option) => /^https?:\/\//.test(option))
   // "features=run,repl,…" shows only these parts (the course builds its
   // profiles from it); without it, everything shows - except "coverage"
-  // (after Tests, the lines no example executed) and "listtree" (lists such
-  // as ["+", 2, 3] also drawn as a tree), which a course switches on
-  // explicitly. "large" enlarges the code and the visualizer, e.g. for a demo
+  // (after Tests, the lines no example executed), "listtree" (lists such
+  // as ["+", 2, 3] also drawn as a tree) and "tree" (the visualizer's mode
+  // «Baum»), which a course switches on explicitly. "large" enlarges the code and the visualizer, e.g. for a demo
   // on the projector.
-  const featureNames = ["run", "tests", "visualize", "reset", "repl", "export", "ide", "coverage", "listtree"]
+  const featureNames = ["run", "tests", "visualize", "reset", "repl", "export", "ide", "coverage", "listtree", "tree"]
   const featuresOption = options.find((option) => option.startsWith("features="))
-  const requestedFeatures = featuresOption ? featuresOption.slice("features=".length).split(",").map((name) => name.trim()).filter(Boolean) : featureNames.filter((name) => name !== "coverage" && name !== "listtree")
+  const requestedFeatures = featuresOption ? featuresOption.slice("features=".length).split(",").map((name) => name.trim()).filter(Boolean) : featureNames.filter((name) => name !== "coverage" && name !== "listtree" && name !== "tree")
   const unknownFeatures = requestedFeatures.filter((name) => !featureNames.includes(name))
   const hasFeature = (name) => requestedFeatures.includes(name)
   const large = options.includes("large")
@@ -1039,7 +1040,8 @@ def quadrat(x):
 The visualizer shows a call to a function whose body is a single `return` either
 as a box or replaced by its return expression (substitution, the default), and
 learners can switch with the toggle in its toolbar. To preset the mode for one
-block, pass `box` or `substitution` to `@GLPython.eval` or `@GLPython.visual`:
+block, pass `box` or `substitution` (or, with the feature `tree`, `tree`) to
+`@GLPython.eval` or `@GLPython.visual`:
 
 ```python
 def quadrat(x):
@@ -1141,6 +1143,18 @@ window, and in the console, where such a value gets a «Baum» button next to
 «Visualisieren». The visualizer's ⋮ menu can switch the trees off («Listen als
 Baum zeigen»). Each tree is described by the list's own text for screen
 readers.
+
+`tree` isn't part of «everything» either. It gives the visualizer a third
+mode, **Baum**, next to «Kasten» and «Ersetzung»: an expression is shown as
+its tree while Python evaluates it. One step replaces the expression by its
+tree, then each step of «Ersetzung» turns a subtree into its value, and one
+step puts the value back in the line - `x = 2 + 3 * 4` takes 5 steps instead
+of 3. A function with a single `return <expression>` is replaced by that
+expression's tree; any other call keeps its box below the tree, which says why
+(«`notenschnitt` hat lokale Variablen – der Aufruf wird als Kasten gezeigt.»,
+also in «Ersetzung»). Labels are Python's (`+`, `quadrat`, `[ ]`), with no
+parentheses. Without `tree` there's no «Baum» button. To start a block in
+«Baum», pass `tree` too: `@GLPython.visual(tree features=visualize,tree)`.
 `large` makes the code 20px (line height 1.6) and the visualizer at least 60% of
 the window, e.g. for the projector in presentation mode.
 
diff --git a/examples/profiles.md b/examples/profiles.md
index d334dbe..e502aee 100644
--- a/examples/profiles.md
+++ b/examples/profiles.md
@@ -20,6 +20,8 @@ import:   https://raw.githubusercontent.com/glpython-edu/glpython-liascript/main
 
 @Code.baum: @GLPython.eval(features=run,repl,visualize,ide,listtree @0)
 
+@Code.ausdruck: @GLPython.eval(features=run,repl,visualize,ide,tree,listtree @0)
+
 @Code.demo: @GLPython.visual(large @0)
 -->
 
@@ -36,6 +38,7 @@ Jede Folie zeigt ein Profil des Kurses. Die Profile sind Makros des Kurses, die
 | pruefung | `features=run`                                 |
 | voll     | (alles)                                        |
 | baum     | `features=run,repl,visualize,ide,listtree`     |
+| ausdruck | `features=run,repl,visualize,ide,tree,listtree` |
 | demo     | `@GLPython.visual(large)`                      |
 
 ## erkunden
@@ -216,6 +219,28 @@ print(ausdruck)
 ```
 @Code.baum
 
+## ausdruck
+
+Der Visualisierer mit dem dritten Modus «Baum»: ein Ausdruck als Baum, Schritt
+für Schritt ausgewertet. `notenschnitt` bleibt ein Kasten, mit dem Hinweis
+warum (auch in «Ersetzung»).
+
+```python
+def quadrat(x):
+    return x * x
+
+def notenschnitt(noten):
+    summe = sum(noten)
+    anzahl = len(noten)
+    return summe / anzahl
+
+x = (2 + 3) * 4
+y = quadrat(2 + 1)
+z = notenschnitt([4, 5, 4.5])
+baum = ["+", 2, ["*", 3, 4]]
+```
+@Code.ausdruck
+
 ## demo
 
 Nur der Visualisierer, gross - für den Projektor.