You can see diagram the attached file.
Diagram has three device with triangle BB#1, BB#2 and L2_Switch.
BB#1 is a root, BB#2 is a root secondary.
L2_Switch is not enabled Spanning-tree protocol.
BB#1 and BB#2 is connected to Port-channel 1 and trunk.
I changed Access port connected L2 Switch to trunk port on BB#2.
I would like to know why this trunk port change stp status block to forwarding for Vlan10?