STEP: flattened hierarchy

[kzhsw]

Describe the bug

After loaded a STEP file, hierarchy in the file is flattened, and only the leaf node is kept.

To Reproduce

1. Load the model here:
   test.zip
2. Look at the Meshes tree in the left of the website

Expected behavior

All hierarchies kept, like in mayo, a desktop OpenCascade-based STEP viewer.

Screenshots