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(function () {
	
	var myApp = angular.module('myApp', []);
	
	myApp.controller('myController', function ($scope) {

		//트리 변환 메서드
		var treeModel = function (arrayList, rootId) {
			var rootNodes = [];
			var traverse = function (nodes, item, index) {
				if (nodes instanceof Array) {
					return nodes.some(function (node) {
						if (node.id === item.parentId) {
							node.children = node.children || [];
							return node.children.push(arrayList.splice(index, 1)[0]);
						}

						return traverse(node.children, item, index);
					});
				}
			};

			while (arrayList.length > 0) {
				arrayList.some(function (item, index) {
					if (item.parentId === rootId) {
						return rootNodes.push(arrayList.splice(index, 1)[0]);
					}

					return traverse(rootNodes, item, index);
				});
			}

			return rootNodes;
		};


		//트리로 변환할 배열
		var list =  [
			{ label : "subUser1", id : "role11", parentId : "role1" },
			{ label : "subUser2-1-1", id : "role1211", parentId : "role121" },
			{ label : "subUser2-1-2", id : "role1212", parentId : "role121" },
			{ label : "Admin", id : "role2", parentId : null },
			{ label : "subUser2", id : "role12", parentId : "role1" },
			{ label : "subUser2-1", id : "role121", parentId : "role12" },
			{ label : "Guest", id : "role3", parentId : null },
      { label : "User", id : "role1", parentId : null }
		];
		$scope.list = JSON.stringify(list, null, '   ');    
    
		//트리 모델로 변환
		var tree = treeModel(list, null);		
		$scope.tree = JSON.stringify(tree, null, '   ');
	});
	
})();

<div ng-app="myApp">
    <div ng-controller="myController">
        <h3>변환할 배열 모델</h3>
        <pre>
{{::list}}
        </pre>
        <h3>변환된 트리 모델</h3>
        <pre>
{{tree}}
        </pre>
    </div>
</div>

pre {
    padding:10px;
    background-color:#EEE; 
    border-radius:5px; 
    line-height: 120%;
    color: #555;
    font-size: 12px;
}