In a hierarchy LOAD, the root nodes should be loaded with parent node being NULL.
Not sure if we need this here, if you want to know what happens if you remove this part, just try it.
edit: I think if you remove the concatenated records, the HIERARCHY LOAD prefix will not work correctly.
From the HELP:
All nodes with a parent id not found in the node id column (including nodes with missing parent id) will be considered as roots. Also, only nodes with a connection to a root node - direct or indirect - will be loaded, thus avoiding circular references.
If a person want to go from B to A , if he selects B in source and A in destination is it possible and if I have a record which shows the information of the train that travels from B to A. In that case what should I do