Set the correct file structure to maintain backward compatibility. (#18)

src/commonMain/kotlin/com.github.adriankuta/datastructure/tree/ChildDeclarationInterface.kt

@@ -0,0 +1,24 @@
+package com.github.adriankuta.datastructure.tree
+
+import kotlin.jvm.JvmSynthetic
+
+interface ChildDeclarationInterface<T> {
+
+    /**
+     * This method is used to easily create child in node.
+     * ```
+     * val root = tree("World") {
+     *     child("North America") {
+     *         child("USA")
+     *     }
+     *     child("Europe") {
+     *         child("Poland")
+     *         child("Germany")
+     *     }
+     * }
+     * ```
+     * @return New created TreeNode.
+     */
+    @JvmSynthetic
+    fun child(value: T, childDeclaration: ChildDeclaration<T>? = null): TreeNode<T>
+}