diff --git a/src/Model/Edge.ts b/src/Model/Edge.ts
index 3eef8ba..92faa77 100644
--- a/src/Model/Edge.ts
+++ b/src/Model/Edge.ts
@@ -5,8 +5,8 @@ export class Edge {
   public name: string
 
   public node!: TreeNode
-  public source: TreeNode | undefined
-  public target: TreeNode | undefined
+  public source?: TreeNode | undefined
+  private cachedHash?: string
 
   constructor(name: string) {
     this.name = name
@@ -17,12 +17,16 @@ export class Edge {
   }
 
   public hash(): string {
-    let previousHash = this.source ? this.source.sourceEdge.hash() : ''
-    return 'H' + sha1(previousHash + this.name)
+    if (!this.cachedHash) {
+      let previousHash = (this.source && this.source.sourceEdge) ? this.source.sourceEdge.hash() : ''
+      this.cachedHash = 'H' + sha1(previousHash + this.name)
+    }
+
+    return this.cachedHash
   }
 
   public firstEdge(): Edge {
-    if (this.source) {
+    if (this.source && this.source.sourceEdge) {
       return this.source.sourceEdge.firstEdge()
     } else {
       return this
diff --git a/src/Model/Tree.ts b/src/Model/Tree.ts
index 155ef1e..2f8bdf0 100644
--- a/src/Model/Tree.ts
+++ b/src/Model/Tree.ts
@@ -2,8 +2,6 @@ import { Edge, TreeNode } from './'
 
 export class Tree extends TreeNode {
   constructor() {
-    const rootEdge = new Edge('')
-    super(rootEdge, undefined)
-    rootEdge.node = this
+    super(undefined, undefined)
   }
 }
diff --git a/src/Model/TreeNode.ts b/src/Model/TreeNode.ts
index 1e356cf..b1e4a3d 100644
--- a/src/Model/TreeNode.ts
+++ b/src/Model/TreeNode.ts
@@ -3,15 +3,17 @@ import { EventEmitter } from 'events'
 
 export class TreeNode extends EventEmitter {
   public sourceEdge?: Edge
-  public value: any | null | undefined = undefined
+  public value?: any | null
   public edges: {[s: string]: Edge} = {}
   public collapsed = false
 
-  constructor(sourceEdge: Edge, value: any) {
+  constructor(sourceEdge?: Edge, value?: any) {
     super()
 
-    this.sourceEdge = sourceEdge
-    sourceEdge.target = this
+    if (sourceEdge) {
+      this.sourceEdge = sourceEdge
+      sourceEdge.target = this
+    }
     this.value = value
   }
 
diff --git a/src/Model/TreeNodeFactory.ts b/src/Model/TreeNodeFactory.ts
index 549b1a9..3255f90 100644
--- a/src/Model/TreeNodeFactory.ts
+++ b/src/Model/TreeNodeFactory.ts
@@ -25,7 +25,7 @@ export abstract class TreeNodeFactory {
     let leaf = reversed[0].node
 
     let sourceTree = new Tree()
-    sourceTree.addEdge(leaf.firstNode().sourceEdge)
+    sourceTree.updateWithNode(leaf.firstNode())
 
     return leaf
   }