Layers are drawn one on top of the others so this is expected.

If you want to show two layers you will have to use transparency (opacity when creating a layer).

However if you want both layers to be simply merged without any visible difference, you will have to merge the data. What prevents you from merging the data? Where is it coming from? The are multiple ways to do it, you can add manually the features to the source (passing a features array when constructing it), you can also create a custom loader.