The Multiple Spanning Tree Protocol (MSTP) is an extension of RSTP that enables VLANs to be grouped into a spanning-tree instance, provides multiple
forwarding paths for data traffic, and enables load balancing  as shown in the next Figure:

MSTP configures a separate spanning tree for each VLAN group allowing to have a configured root bridge and forwarding topology for each VLAN. It blocks all but one possible alternate path within each spanning tree.  SoC-e switching IPs can support up to 4096 Spanning Trees.