diff --git a/bkl.go b/bkl.go
index 5aee91f..8ad0187 100644
--- a/bkl.go
+++ b/bkl.go
@@ -52,6 +52,19 @@ func (p *Parser) SetDebug(debug bool) {
 	p.debug = debug
 }
 
+// MergeOther applies other's internal document state to ours, using bkl's
+// merge semantics.
+func (p *Parser) MergeOther(other *Parser) error {
+	for i, doc := range other.docs {
+		err := p.MergePatch(i, doc)
+		if err != nil {
+			return err
+		}
+	}
+
+	return nil
+}
+
 // MergePatch applies the supplied patch to the [Parser]'s current internal
 // document state (at the specified document index) using bkl's merge
 // semantics.
diff --git a/cmd/bkl/main.go b/cmd/bkl/main.go
index 0d50f3f..50c369d 100644
--- a/cmd/bkl/main.go
+++ b/cmd/bkl/main.go
@@ -35,7 +35,12 @@ func main() {
 	}
 
 	for _, path := range opts.Positional.InputPaths {
-		err := p.MergeFileLayers(path)
+		fileP, err := bkl.NewFromFile(path)
+		if err != nil {
+			fatal("%s", err)
+		}
+
+		err = p.MergeOther(fileP)
 		if err != nil {
 			fatal("%s", err)
 		}
diff --git a/tests/tree/expected b/tests/tree/expected
index e69de29..49271ae 100644
--- a/tests/tree/expected
+++ b/tests/tree/expected
@@ -0,0 +1,4 @@
+a: 1
+b: 2
+c: 3
+d: 4