Convert a List of Nodes to a single Node where the subsequent nodes in the List are the children of the predecessor.

ListToHierarchy.groovy

class Node {
    String name
    Node child
    
    static Node asHierarchy(List<Node> nodes) {
        nodes.reverse().inject(null) { prev, curr ->
            curr.child = prev
            curr
        }
    }
}

def nodes = ['A','B','C'].collect { new Node(name: it) }
def (nodeA, nodeB, nodeC) = nodes

// convert list into hierarchy
def top = Node.asHierarchy(nodes)

assert top == nodeA
assert nodeA.child == nodeB
assert nodeB.child == nodeC
assert nodeC.child == null