diff --git a/.gitmodules b/.gitmodules
new file mode 100644
index 0000000..20f09e0
--- /dev/null
+++ b/.gitmodules
@@ -0,0 +1,3 @@
+[submodule "submodule_demo"]
+	path = submodule_demo
+	url = https://gitea.hmac.kr/chan/test_subtree.git
diff --git a/submodule_demo b/submodule_demo
new file mode 160000
index 0000000..4068f8d
--- /dev/null
+++ b/submodule_demo
@@ -0,0 +1 @@
+Subproject commit 4068f8ddfb6b69c82ab8afe18a75894998c1fdbc