diff --git a/libmultilabel/linear/tree.py b/libmultilabel/linear/tree.py
index 64070b2a..0db2f868 100644
--- a/libmultilabel/linear/tree.py
+++ b/libmultilabel/linear/tree.py
@@ -289,7 +289,7 @@ def visit(node):
 
     model = linear.FlatModel(
         name="flattened-tree",
-        weights=sparse.hstack(weights, "csr"),
+        weights=sparse.hstack(weights, "csc"),
         bias=bias,
         thresholds=0,
         multiclass=False,