A minimal recursive tree directive for Angular.js. Demo: http://jsfiddle.net/furf/EJGHX/

0-angular-tree.js

var app = angular.module('app', []);

app.directive('yaTree', function () {

  return {
    restrict: 'A',
    transclude: 'element',
    priority: 1000,
    terminal: true,
    compile: function (tElement, tAttrs, transclude) {

      var repeatExpr, childExpr, rootExpr, childrenExpr;

      repeatExpr = tAttrs.yaTree.match(/^(.*) in ((?:.*\.)?(.*)) at (.*)$/);
      childExpr = repeatExpr[1];
      rootExpr = repeatExpr[2];
      childrenExpr = repeatExpr[3];
      branchExpr = repeatExpr[4];

      return function link (scope, element, attrs) {

        var rootElement = element[0].parentNode,
            cache = [];

        // Reverse lookup object to avoid re-rendering elements
        function lookup (child) {
          var i = cache.length;
          while (i--) {
            if (cache[i].scope[childExpr] === child) {
              return cache.splice(i, 1)[0];
            }
          }
        }

        scope.$watch(rootExpr, function (root) {

          var currentCache = [];

          // Recurse the data structure
          (function walk (children, parentNode, parentScope, depth) {

            var i = 0,
                n = children.length,
                last = n - 1,
                cursor,
                child,
                cached,
                childScope,
                grandchildren;

            // Iterate the children at the current level
            for (; i < n; ++i) {

              // We will compare the cached element to the element in 
              // at the destination index. If it does not match, then 
              // the cached element is being moved into this position.
              cursor = parentNode.childNodes[i];

              child = children[i];

              // See if this child has been previously rendered
              // using a reverse lookup by object reference
              cached = lookup(child);
              
              // If the parentScope no longer matches, we've moved.
              // We'll have to transclude again so that scopes 
              // and controllers are properly inherited
              if (cached && cached.parentScope !== parentScope) {
                cache.push(cached);
                cached = null;
              }
              
              // If it has not, render a new element and prepare its scope
              // We also cache a reference to its branch node which will
              // be used as the parentNode in the next level of recursion
              if (!cached) {
                transclude(parentScope.$new(), function (clone, childScope) {

                  childScope[childExpr] = child;
                  
                  cached = {
                    scope: childScope,
                    parentScope: parentScope,
                    element: clone[0],
                    branch: clone.find(branchExpr)[0]
                  };

                  // This had to happen during transclusion so inherited 
                  // controllers, among other things, work properly
                  parentNode.insertBefore(cached.element, cursor);

                });
              } else if (cached.element !== cursor) {
                parentNode.insertBefore(cached.element, cursor);
              }

              // Lets's set some scope values
              childScope = cached.scope;

              // Store the current depth on the scope in case you want 
              // to use it (for good or evil, no judgment).
              childScope.$depth = depth;
              
              // Emulate some ng-repeat values
              childScope.$index = i;
              childScope.$first = (i === 0);
              childScope.$last = (i === last);
              childScope.$middle = !(childScope.$first || childScope.$last);

              // Push the object onto the new cache which will replace
              // the old cache at the end of the walk.
              currentCache.push(cached);

              // If the child has children of its own, recurse 'em.             
              grandchildren = child[childrenExpr];
              if (grandchildren && grandchildren.length) {
                walk(grandchildren, cached.branch, childScope, depth + 1);
              }
            }
          })(root, rootElement, scope, 0);

          // Cleanup objects which have been removed.
          // Remove DOM elements and destroy scopes to prevent memory leaks.
          i = cache.length;

          while (i--) {
            cached = cache[i];
            if (cached.scope) {
              cached.scope.$destroy();
            }
            if (cached.element) {
              cached.element.parentNode.removeChild(cached.element);
            } 
          }

          // Replace previous cache.
          cache = currentCache;

        }, true);
      };
    }
  };
});


app.controller('TreeController', function ($scope, $timeout) {
    $scope.json = '';
  $scope.data = {
    children: [{
      title: 'hello, world',
        children: [{
            title: 'test 1',
            children: []
        },
        {
            title: 'test 2',
            children: []
        }]
    }]
  };
    
    $scope.getJson = function () {
        $scope.json = angular.toJson($scope.data);
    };
    
  $scope.toggleMinimized = function (child) {
    child.minimized = !child.minimized;
  };
    
  $scope.addChild = function (child) {
    child.children.push({
      title: '',
      children: []
    });
  };

  $scope.remove = function (child) {
    function walk(target) {
      var children = target.children,
        i;
      if (children) {
        i = children.length;
        while (i--) {
          if (children[i] === child) {
            return children.splice(i, 1);
          } else {
            walk(children[i])
          }
        }
      }
    }
    walk($scope.data);
  }

  $scope.update = function (event, ui) {

    var root = event.target,
      item = ui.item,
      parent = item.parent(),
      target = (parent[0] === root) ? $scope.data : parent.scope().child,
      child = item.scope().child,
      index = item.index();

    target.children || (target.children = []);

    function walk(target, child) {
      var children = target.children,
        i;
      if (children) {
        i = children.length;
        while (i--) {
          if (children[i] === child) {
            return children.splice(i, 1);
          } else {
            walk(children[i], child);
          }
        }
      }
    }
    walk($scope.data, child);

    target.children.splice(index, 0, child);
  };

});

1-angular-tree.css

[ng-cloak] {
  display: none;
}
* {
  box-sizing: border-box
}
body {
  font: 12px/16px helvetica, arial, sans-serif;
  background: #eee;
}
ol {
  margin:4px 0;
  border: 0 none transparent;
  padding: 0;
  background:#eee;
}
li {
  list-style:none;
  margin: 1px;
  border: 1px solid #ddd;
  padding: 8px 8px 4px 8px;
  background: #fff;
}
.ui-sortable li {
  cursor: move;
}
.live input, .shadow input {
  margin: 0;
  border: 1px solid #ddd;
  padding: 1px;
  font: inherit;
  font-weight: bold;
  height:2em;
}
.ui-state-highlight {
  border: 1px solid #fc0;
  background: #ffe;
}
.live, .shadow {
  float: left;
  width: 45%;
  margin-right: 5%;
}
.shadow {
  opacity: 0.7;
}
.debug {
  clear: both;
}
.debug textarea {
  width: 100%;
  height: 40em;
  font: 10px/13px monospace;
}
textarea, input {
  outline: none;
}
.pregnant {
  border: 1px solid #ddd;
}
.bg0 { background:#fcc; }
.bg1 { background:#ffc; }
.bg2 { background:#cfc; }
.bg3 { background:#cff; }
.bg4 { background:#ccf; }
.bg5 { background:#fcf; }
.minimized > ol > li { display:none; }
.minimized > ol {   border: 0 none transparent; }
.toggle { border: 0 none transparent; background:transparent; width:2em; color:#aaa; }
button { cursor: pointer }

2-angular-tree.html

<script type='text/javascript' src='//code.jquery.com/jquery-1.9.1.js'></script>
<script type="text/javascript" src="http://code.jquery.com/ui/1.9.2/jquery-ui.js"></script>
<link rel="stylesheet" type="text/css" href="http://code.jquery.com/ui/1.9.2/themes/base/jquery-ui.css">
<script type='text/javascript' src="http://cdnjs.cloudflare.com/ajax/libs/jqueryui-touch-punch/0.2.2/jquery.ui.touch-punch.min.js"></script>
<script type='text/javascript' src="https://raw.github.com/mjsarfatti/nestedSortable/master/jquery.mjs.nestedSortable.js"></script>
<script type='text/javascript' src="http://cdnjs.cloudflare.com/ajax/libs/angular.js/1.1.1/angular.min.js"></script>

<div ng-app="app" ng-cloak>
  <div ng-controller="TreeController">
    <div>
      <button ng-click="addChild(data)">+ New</button>
    </div>
    <div class="live">
      <ol>
        <li ya-tree="child in data.children at ol" ng-class="{minimized:child.minimized}">
          <div>
            <button class="toggle" ng-click="toggleMinimized(child)" ng-switch on="child.minimized"><span ng-switch-when="true">&#x25B6;</span><span ng-switch-default>&#x25BC;</span></button>
            <input ng-model="child.title" />
            <button ng-click="addChild(child)">+</button>
            <button ng-click="remove(child)">x</button>
          </div>
          <ol ng-class="{pregnant:child.children.length}"></ol>
        </li>
      </ol>
    </div>
    <div class="shadow">
      <ol>
        <li ya-tree="child in data.children at ol" class="bg{{$depth%6}}" ng-class="{minimized:child.minimized}">
          <div>
            <input disabled value="{{child.title}}" /> <em>({{$depth}})</em>
          </div>
          <ol ng-class="{pregnant:child.children.length}"></ol>
        </li>
      </ol>
    </div>
      <div><button ng-click="getJson()">Json</button></div>
    <div>{{json}}</div>
  </div>
</div>