File structure on left pane and changes to directory when you open file

application/src/main/kotlin/net/codebot/application/FolderView.kt

@@ -8,14 +8,14 @@ import javafx.scene.layout.StackPane
 import java.io.File
 
 class FolderView {
-    fun build() : StackPane {
+    fun build(pathname: String = "src/main/kotlin") : StackPane {
         val folder_img = ImageView(Image("https://png.pngtree.com/png-vector/20190916/ourmid/pngtree-folder-icon-for-your-project-png-image_1731079.jpg"))
         folder_img.fitWidth = 20.0
         folder_img.fitHeight = 20.0
         val folderIcon: Node = folder_img
         val rootItem = TreeItem<Any?>("Inbox", folderIcon)
         rootItem.isExpanded = true
-        File("src/main/kotlin").walk(FileWalkDirection.BOTTOM_UP).forEach {
+        File(pathname).walk(FileWalkDirection.BOTTOM_UP).forEach {
             val item = TreeItem<Any?>(it)
             rootItem.children.add(item)
         }

application/src/main/kotlin/net/codebot/application/Main.kt

@@ -52,7 +52,9 @@ class Main : Application() {
         val status = HBox(label)
 
         // code for left pane
-        val left = VBox(Text("Left Pane"))
+        val tree = FolderView().build()
+        val left = tree
+        left.prefWidth = 250.0
 
         // code for right pane
         val display_text = TextArea()
@@ -62,7 +64,7 @@ class Main : Application() {
         display_text.prefColumnCount = 200
         display_text.isEditable = false
         val right = HBox(display_text)
-        right.prefWidth = 750.0
+        right.prefWidth = 650.0
 
         bold.setOnMouseClicked {
             var currentHighlight = text.selectedText
@@ -153,7 +155,7 @@ class Main : Application() {
             } catch (e: FileNotFoundException) {
                 e.printStackTrace();
             }
-
+            border.left = FolderView().build(selectedFile.parentFile.absolutePath)
         }
 
         border.top = topContainer