Actually add the file

lua/custom/plugins/filetree.lua

@@ -0,0 +1,14 @@
+vim.cmd([[ let g:neo_tree_remove_legacy_commands = 1 ]])
+
+return {
+  "nvim-neo-tree/neo-tree.nvim",
+  version = "*",
+  dependencies = {
+    "nvim-lua/plenary.nvim",
+    "nvim-tree/nvim-web-devicons", -- not strictly required, but recommended
+    "MunifTanjim/nui.nvim",
+  },
+  config = function()
+    require('neo-tree').setup {}
+  end,
+}