diff --git a/lib/arbor/tree.ex b/lib/arbor/tree.ex
index db31dcf..2ab71b5 100644
--- a/lib/arbor/tree.ex
+++ b/lib/arbor/tree.ex
@@ -35,7 +35,12 @@ defmodule Arbor.Tree do
   defmacro __before_compile__(%{module: definition} = _env) do
     arbor_opts = Module.get_attribute(definition, :arbor_opts)
 
-    {primary_key, primary_key_type, _} = Module.get_attribute(definition, :primary_key)
+
+    {primary_key, primary_key_type} = case Module.get_attribute(definition, :primary_key) do
+        {primary_key, primary_key_type, _} -> {primary_key, primary_key_type}
+        _ -> {arbor_opts[:primary_key], arbor_opts[:primary_key_type]}
+      end
+
     struct_fields = Module.get_attribute(definition, :struct_fields)
 
     struct_source = struct_fields[:__meta__].source
@@ -80,13 +85,15 @@ defmodule Arbor.Tree do
         )
       end
 
+      defp id(struct), do: Map.get(struct, unquote(opts[:foreign_key]), Map.get(struct, :id))
+
       def parent(struct) do
         from(
           t in unquote(definition),
           where:
             fragment(
               unquote("#{opts[:primary_key]} = ?"),
-              type(^struct.unquote(opts[:foreign_key]), unquote(opts[:foreign_key_type]))
+              type(^id(struct), unquote(opts[:foreign_key_type]))
             )
         )
       end
@@ -97,7 +104,7 @@ defmodule Arbor.Tree do
           where:
             fragment(
               unquote("#{opts[:foreign_key]} = ?"),
-              type(^struct.unquote(opts[:primary_key]), unquote(opts[:foreign_key_type]))
+              type(^id(struct), unquote(opts[:foreign_key_type]))
             )
         )
       end
@@ -107,7 +114,7 @@ defmodule Arbor.Tree do
           t in unquote(definition),
           where:
             t.unquote(opts[:primary_key]) !=
-              type(^struct.unquote(opts[:primary_key]), unquote(opts[:primary_key_type])),
+              type(^id(struct), unquote(opts[:primary_key_type])),
           where:
             fragment(
               unquote("#{opts[:foreign_key]} = ?"),
@@ -137,7 +144,7 @@ defmodule Arbor.Tree do
             SELECT *
             FROM #{opts[:tree_name]}
           )
-          """), type(^struct.unquote(opts[:primary_key]), unquote(opts[:primary_key_type]))),
+          """), type(^id(struct), unquote(opts[:primary_key_type]))),
           on: t.unquote(opts[:primary_key]) == g.unquote(opts[:foreign_key])
       end
 
@@ -164,7 +171,7 @@ defmodule Arbor.Tree do
               )
               SELECT #{opts[:primary_key]} FROM #{opts[:tree_name]}
               """),
-              type(^struct.unquote(opts[:primary_key]), unquote(opts[:foreign_key_type])),
+              type(^id(struct), unquote(opts[:foreign_key_type])),
               type(^depth, :integer)
             )
         )