diff --git a/lib/mb_binary_tree.ex b/lib/mb_binary_tree.ex
index efb41b7..ba375c1 100644
--- a/lib/mb_binary_tree.ex
+++ b/lib/mb_binary_tree.ex
@@ -1,3 +1,5 @@
+import Kernel, except: [length: 1]
+
 defmodule MbBinaryTree do
   @moduledoc """
   Documentation for `MbBinaryTree`.
@@ -40,6 +42,58 @@ defmodule MbBinaryTree do
   def is_tree?([_, left, right]), do: is_tree?(left) && is_tree?(right)
   def is_tree?(_), do: false
 
+  @spec is_empty?(t) :: boolean
+  @doc """
+  Check if a binary tree is empty.
+
+  ## Examples
+
+      iex> MbBinaryTree.is_empty?(nil)
+      true
+      iex> MbBinaryTree.new("hello") |> MbBinaryTree.is_empty?()
+      false
+  """
+  def is_empty?(nil), do: true
+  def is_empty?(_), do: false
+
+  @spec length(t) :: non_neg_integer
+  @doc """
+  Get the length of a tree.
+
+  ## Examples
+
+      iex> MbBinaryTree.length([1, MbBinaryTree.new(2), MbBinaryTree.new(3)])
+      3
+      iex> MbBinaryTree.length([12, [4, MbBinaryTree.new(2), MbBinaryTree.new(5)], [26, MbBinaryTree.new(14), [28, MbBinaryTree.new(27), MbBinaryTree.new(30)]]])
+      9
+  """
+  def length([_ | [left, right]]), do: 1 + length(left) + length(right)
+  def length(_), do: 0
+
+  @doc """
+  Calculate the depth of a binary tree.
+
+  ## Examples
+
+      iex> MbBinaryTree.depth(nil)
+      0
+      iex> MbBinaryTree.depth([1, nil, nil])
+      1
+      iex> MbBinaryTree.depth([1, [2, nil, nil], [3, nil, nil]])
+      2
+      iex> MbBinaryTree.depth([1, [2, nil, nil], [3, [4, nil, nil], [5, nil, nil]]])
+      3
+      iex> MbBinaryTree.depth([12, [4, MbBinaryTree.new(2), MbBinaryTree.new(5)], [26, MbBinaryTree.new(14), [28, MbBinaryTree.new(27), MbBinaryTree.new(30)]]])
+      4
+  """
+  def depth(tree) do
+    case tree do
+      nil -> 0
+      [_, nil, nil] -> 1
+      [_, left, right] -> 1 + max(depth(left), depth(right))
+    end
+  end
+
   @spec left(t) :: t
   @doc """
   Get the left child of a tree.
@@ -97,28 +151,4 @@ defmodule MbBinaryTree do
       [12, nil, [4, nil, nil]]
   """
   def update_right([node, left, _right], new_right), do: [node, left, new_right]
-
-  @doc """
-  Calculate the depth of a binary tree.
-
-  ## Examples
-
-      iex> MbBinaryTree.depth(nil)
-      0
-      iex> MbBinaryTree.depth([1, nil, nil])
-      1
-      iex> MbBinaryTree.depth([1, [2, nil, nil], [3, nil, nil]])
-      2
-      iex> MbBinaryTree.depth([1, [2, nil, nil], [3, [4, nil, nil], [5, nil, nil]]])
-      3
-      iex> MbBinaryTree.depth([12, [4, MbBinaryTree.new(2), MbBinaryTree.new(5)], [26, MbBinaryTree.new(14), [28, MbBinaryTree.new(27), MbBinaryTree.new(30)]]])
-      4
-  """
-  def depth(tree) do
-    case tree do
-      nil -> 0
-      [_, nil, nil] -> 1
-      [_, left, right] -> 1 + max(depth(left), depth(right))
-    end
-  end
 end