Ensure stable plugins get installed. (#1373)

crates/nu_plugin_tree/src/nu/mod.rs

@@ -0,0 +1,21 @@
+use nu_errors::ShellError;
+use nu_plugin::Plugin;
+use nu_protocol::{CallInfo, Signature, Value};
+
+use crate::tree::TreeView;
+use crate::TreeViewer;
+
+impl Plugin for TreeViewer {
+    fn config(&mut self) -> Result<Signature, ShellError> {
+        Ok(Signature::build("tree").desc("View the contents of the pipeline as a tree."))
+    }
+
+    fn sink(&mut self, _call_info: CallInfo, input: Vec<Value>) {
+        if !input.is_empty() {
+            for i in input.iter() {
+                let view = TreeView::from_value(&i);
+                let _ = view.render_view();
+            }
+        }
+    }
+}