diff --git a/expandable-recyclerview/build.gradle b/expandable-recyclerview/build.gradle
index 44749ad..04d0d67 100644
--- a/expandable-recyclerview/build.gradle
+++ b/expandable-recyclerview/build.gradle
@@ -15,7 +15,7 @@ android {
         minSdkVersion 23
         targetSdkVersion 29
         versionCode 1
-        versionName "0.0.1-alpha02"
+        versionName "0.0.1-beta01"
 
         testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"
         consumerProguardFiles 'consumer-rules.pro'
diff --git a/expandable-recyclerview/src/main/java/com/github/adriankuta/expandable_recyclerview/ExpandableTreeNode.kt b/expandable-recyclerview/src/main/java/com/github/adriankuta/expandable_recyclerview/ExpandableTreeNode.kt
index e45ae54..f321d1b 100644
--- a/expandable-recyclerview/src/main/java/com/github/adriankuta/expandable_recyclerview/ExpandableTreeNode.kt
+++ b/expandable-recyclerview/src/main/java/com/github/adriankuta/expandable_recyclerview/ExpandableTreeNode.kt
@@ -6,33 +6,77 @@ import com.github.adriankuta.datastructure.tree.TreeNode
 class ExpandableTreeNode<T>(value: T) : TreeNode<T>(value) {
 
     var expanded: Boolean = true
-        set(value) {
-            field = value
-            children.forEach {
-                (it as ExpandableTreeNode).expanded = value
-            }
-        }
 
-    override fun child(value: T, childDeclaration: ChildDeclaration<T>?) {
-        val newChild = ExpandableTreeNode(value)
+    override fun child(child: T, childDeclaration: ChildDeclaration<T>?) {
+        val newChild = ExpandableTreeNode(child)
         if (childDeclaration != null)
             newChild.childDeclaration()
         addChild(newChild)
     }
 
-    fun getVisibleNodeCount(): Int {
-        return onlyVisibleItems()
+    /**
+     * @param skipRootNode If `True`, then root node won't be counted.
+     */
+    internal fun getVisibleNodeCount(skipRootNode: Boolean): Int {
+        var size = onlyVisibleItems()
             .size
+
+        if (skipRootNode && size > 0)
+            size--
+
+        return size
     }
 
-    fun getVisibleNode(position: Int): ExpandableTreeNode<T> {
-        return onlyVisibleItems()[position]
+    /**
+     * This function use Pre-order iteration to go through tree:
+     * ```
+     * e.g.
+     *                    1
+     *                  / | \
+     *                 /  |   \
+     *               2    3     4
+     *              / \       / | \
+     *             5    6    7  8  9
+     *            /   / | \
+     *           10  11 12 13
+     *
+     * Output (skipRootNode = false): 1 2 5 10 6 11 12 13 3 4 7 8 9
+     * Output (skipRootNode = true): 2 5 10 6 11 12 13 3 4 7 8 9
+     * ```
+     * @param skipRootNode If `True` root element will be omitted, and position 0 will be for first left child.
+     */
+    internal fun getVisibleNode(position: Int, skipRootNode: Boolean): ExpandableTreeNode<T> {
+        val nodePosition = if (skipRootNode) position + 1 else position
+        return onlyVisibleItems()[nodePosition]
     }
 
+    /**
+     * @return List of nodes which parent or higher ancestor aren't collapsed.
+     */
     private fun onlyVisibleItems(): List<ExpandableTreeNode<T>> {
         //Visible if parent of node is expanded.
         return map { it as ExpandableTreeNode }
-            .filter { (it.parent as? ExpandableTreeNode)?.expanded ?: true }
+            .filter { allAncestorsAreExpanded(it) }
+    }
+
+    /**
+     * `Ancestor` is a node reachable by repeated proceeding from child to parent.
+     * @return `True` if parent, and all parent's ancestors are expanded.
+     */
+    private fun allAncestorsAreExpanded(node: ExpandableTreeNode<T>): Boolean {
+        var ancestor = parent as? ExpandableTreeNode
+        var ancestorsAreExpanded = isAncestorExpanded(ancestor)
+
+        while (ancestorsAreExpanded && ancestor != null) {
+            ancestor = ancestor.parent as? ExpandableTreeNode<T>
+            ancestorsAreExpanded = ancestorsAreExpanded.and(isAncestorExpanded(ancestor))
+        }
+
+        return ancestorsAreExpanded
+    }
+
+    private fun isAncestorExpanded(ancestor: ExpandableTreeNode<T>?): Boolean {
+        return ancestor?.expanded ?: true
     }
 
 }
\ No newline at end of file
diff --git a/expandable-recyclerview/src/main/java/com/github/adriankuta/expandable_recyclerview/MultilevelRecyclerViewAdapter.kt b/expandable-recyclerview/src/main/java/com/github/adriankuta/expandable_recyclerview/MultilevelRecyclerViewAdapter.kt
index 9a37046..0e80119 100644
--- a/expandable-recyclerview/src/main/java/com/github/adriankuta/expandable_recyclerview/MultilevelRecyclerViewAdapter.kt
+++ b/expandable-recyclerview/src/main/java/com/github/adriankuta/expandable_recyclerview/MultilevelRecyclerViewAdapter.kt
@@ -12,25 +12,35 @@ abstract class MultilevelRecyclerViewAdapter<T, VH : RecyclerView.ViewHolder> :
     abstract override fun onCreateViewHolder(parent: ViewGroup, nestLevel: Int): VH
 
     final override fun onBindViewHolder(holder: VH, position: Int) {
-        onBindViewHolder(holder, treeNodes.getVisibleNode(position))
+        val visibleNode = treeNodes.getVisibleNode(position, true)
+        onBindViewHolder(holder, visibleNode, visibleNode.depth())
     }
 
-    abstract fun onBindViewHolder(holder: VH, treeNode: ExpandableTreeNode<T>)
+    abstract fun onBindViewHolder(holder: VH, treeNode: ExpandableTreeNode<T>, nestLevel: Int)
 
     abstract fun getTreeNodes(): ExpandableTreeNode<T>
 
     final override fun getItemCount(): Int {
         treeNodes = getTreeNodes()
-        return treeNodes.getVisibleNodeCount()
+        return treeNodes.getVisibleNodeCount(true) //We don't want to show root element.
     }
 
     final override fun getItemViewType(position: Int): Int {
-
-        return treeNodes.getVisibleNode(position).depth()
+        return treeNodes.getVisibleNode(position, true).depth()
     }
 
     fun toggleGroup(expandableTreeNode: ExpandableTreeNode<T>) {
         expandableTreeNode.expanded = !expandableTreeNode.expanded
         notifyDataSetChanged()
     }
+
+    fun expand(expandableTreeNode: ExpandableTreeNode<T>) {
+        expandableTreeNode.expanded = true
+        notifyDataSetChanged()
+    }
+
+    fun collapse(expandableTreeNode: ExpandableTreeNode<T>) {
+        expandableTreeNode.expanded = false
+        notifyDataSetChanged()
+    }
 }
\ No newline at end of file