diff --git a/luminos_lib/tree.py b/luminos_lib/tree.py
new file mode 100644
index 0000000..4cc67d9
--- /dev/null
+++ b/luminos_lib/tree.py
@@ -0,0 +1,83 @@
+"""Directory tree visualization."""
+
+import os
+
+
+def build_tree(path, max_depth=3, show_hidden=False, _depth=0):
+    """Build a nested dict representing the directory tree with file sizes."""
+    name = os.path.basename(path) or path
+    node = {"name": name, "path": path, "type": "directory", "children": []}
+
+    try:
+        entries = sorted(os.listdir(path))
+    except PermissionError:
+        node["error"] = "permission denied"
+        return node
+
+    for entry in entries:
+        if not show_hidden and entry.startswith("."):
+            continue
+        full = os.path.join(path, entry)
+        if os.path.isdir(full):
+            if _depth < max_depth:
+                child = build_tree(full, max_depth, show_hidden, _depth + 1)
+                node["children"].append(child)
+            else:
+                node["children"].append({
+                    "name": entry, "path": full,
+                    "type": "directory", "truncated": True,
+                })
+        elif os.path.isfile(full):
+            try:
+                size = os.path.getsize(full)
+            except OSError:
+                size = 0
+            node["children"].append({
+                "name": entry, "path": full,
+                "type": "file", "size": size,
+            })
+
+    return node
+
+
+def _human_size(nbytes):
+    """Convert bytes to human-readable string."""
+    for unit in ("B", "KB", "MB", "GB", "TB"):
+        if nbytes < 1024:
+            if unit == "B":
+                return f"{nbytes} {unit}"
+            return f"{nbytes:.1f} {unit}"
+        nbytes /= 1024
+    return f"{nbytes:.1f} PB"
+
+
+def render_tree(node, prefix="", is_last=True, is_root=True):
+    """Render the tree dict as a visual string."""
+    lines = []
+
+    if is_root:
+        lines.append(f"{node['name']}/")
+    else:
+        connector = "\u2514\u2500\u2500 " if is_last else "\u251c\u2500\u2500 "
+        label = node["name"]
+        if node["type"] == "file":
+            label += f"  ({_human_size(node.get('size', 0))})"
+        elif node.get("truncated"):
+            label += "/  ..."
+        elif node["type"] == "directory":
+            label += "/"
+        if node.get("error"):
+            label += f"  [{node['error']}]"
+        lines.append(prefix + connector + label)
+
+    children = node.get("children", [])
+    for i, child in enumerate(children):
+        if is_root:
+            child_prefix = ""
+        else:
+            child_prefix = prefix + ("    " if is_last else "\u2502   ")
+        lines.append(
+            render_tree(child, child_prefix, i == len(children) - 1, False)
+        )
+
+    return "\n".join(lines)