Nuke: Vertical Merge

nvm.py

import nuke


x_separation = 110
y_separation = 110

selection = {}
for node in nuke.allNodes():
    if node["selected"].value():
        selection[node.name()] = node

sorted_keys = list(reversed(sorted(selection.keys())))
first_node = selection[sorted_keys[0]]
previous_node = first_node
for key in sorted_keys[1:]:
    index = sorted_keys.index(key)
    node = selection[key]
    y_pos = first_node.ypos() + (index * y_separation)
    node.setXYpos(first_node.xpos(), y_pos)

    merge_node = nuke.createNode("Merge")
    merge_node.setXYpos(node.xpos() + x_separation, y_pos + (node.screenHeight() / 2) - (merge_node.screenHeight() / 2))

    merge_node.setInput(0, previous_node)
    merge_node.setInput(1, node)

    previous_node = merge_node