following the simple code, you can build a tree.
final NodeModel<String> nodeA = new NodeModel<>("A");
final NodeModel<String> nodeB = new NodeModel<>("B");
final NodeModel<String> nodeC = new NodeModel<>("C");
final NodeModel<String> nodeD = new NodeModel<>("D");
final NodeModel<String> nodeE = new NodeModel<>("E");
final NodeModel<String> nodeF = new NodeModel<>("F");
final NodeModel<String> nodeG = new NodeModel<>("G");
final NodeModel<String> nodeH = new NodeModel<>("H");
final NodeModel<String> nodeI = new NodeModel<>("I");
final NodeModel<String> nodeJ = new NodeModel<>("J");
final NodeModel<String> nodeK = new NodeModel<>("K");
final NodeModel<String> nodeL = new NodeModel<>("L");
final NodeModel<String> nodeM = new NodeModel<>("M");
final NodeModel<String> nodeN = new NodeModel<>("N");
final NodeModel<String> nodeO = new NodeModel<>("O");
final NodeModel<String> nodeP = new NodeModel<>("P");
final NodeModel<String> nodeQ = new NodeModel<>("Q");
final NodeModel<String> nodeR = new NodeModel<>("R");
final NodeModel<String> nodeS = new NodeModel<>("S");
final NodeModel<String> nodeT = new NodeModel<>("T");
final NodeModel<String> nodeU = new NodeModel<>("U");
final NodeModel<String> nodeV = new NodeModel<>("V");
final NodeModel<String> nodeW = new NodeModel<>("W");
final NodeModel<String> nodeX = new NodeModel<>("X");
final NodeModel<String> nodeY = new NodeModel<>("Y");
final NodeModel<String> nodeZ = new NodeModel<>("Z");
final TreeModel<String> tree = new TreeModel<>(nodeA);
tree.addNode(nodeA, nodeB, nodeC, nodeD);
tree.addNode(nodeC, nodeE, nodeF, nodeG, nodeH, nodeI);
tree.addNode(nodeB, nodeJ, nodeK, nodeL);
tree.addNode(nodeD, nodeM, nodeN, nodeO);
tree.addNode(nodeF, nodeP, nodeQ, nodeR, nodeS);
tree.addNode(nodeR, nodeT, nodeU, nodeV, nodeW, nodeX);
tree.addNode(nodeT, nodeY, nodeZ);
int dx = DensityUtils.dp2px(this, 20);
int dy = DensityUtils.dp2px(this, 20);
int mHeight = DensityUtils.dp2px(this, 720);
testTreeView.setTreeLayoutManager(new RightTreeLayoutManager(dx, dy, mHeight));
testTreeView.setTreeModel(tree);