Example.cs

using System.Collections.Generic;
using UnityEditor;
using UnityEngine;

[InitializeOnLoad]
public static class Example
{
    private const int WIDTH          = 16;
    private const int START_OFFSET_X = -22;
    private const int OFFSET_X       = -14;

    private static readonly Color COLOR = new Color32( 104, 104, 104, 255 );

    private static readonly Dictionary<string, Texture> m_textureTable = new Dictionary<string, Texture>();

    static Example()
    {
        EditorApplication.hierarchyWindowItemOnGUI += OnGUI;
    }

    private static void OnGUI( int instanceID, Rect selectionRect )
    {
        var gameObject = EditorUtility.InstanceIDToObject( instanceID ) as GameObject;

        if ( gameObject == null ) return;

        var parent = gameObject.transform.parent;

        if ( parent == null ) return;

        var position = selectionRect;

        position.width =  WIDTH;
        position.x     += START_OFFSET_X;

        var oldColor = GUI.color;

        GUI.color = COLOR;

        if ( parent.childCount == 1 ||
             parent.GetChild( parent.childCount - 1 ) == gameObject.transform )
        {
            DrawTexture( position, "Assets/border003.png" );
        }
        else
        {
            DrawTexture( position, "Assets/border002.png" );
        }

        while ( parent != null )
        {
            var parentParent = parent.parent;

            if ( parentParent == null ) break;

            if ( parent == parentParent.GetChild( parentParent.childCount - 1 ) )
            {
                parent     =  parentParent;
                position.x += OFFSET_X;
                continue;
            }

            position.x += OFFSET_X;

            DrawTexture( position, "Assets/border001.png" );

            parent = parentParent;
        }

        GUI.color = oldColor;
    }

    private static void DrawTexture( Rect position, string path )
    {
        var image = LoadTexture( path );
        GUI.DrawTexture( position, image, ScaleMode.ScaleToFit );
    }

    private static Texture LoadTexture( string path )
    {
        if ( m_textureTable.TryGetValue( path, out var result ) ) return result;
        var texture = ( Texture ) EditorGUIUtility.Load( path );
        m_textureTable[ path ] = texture;
        return texture;
    }
}

Texture