csharp
using Umbraco.Cms.Core;
using Umbraco.Cms.Core.Models.ContentEditing;

namespace Umbraco.Trees
{
    public class FavouriteeThingsTree : Umbraco.Cms.Core.Trees.ISearchableTree
    {
        public string TreeAlias => "favouriteeThingsAlias";

        public async Task<EntitySearchResults> SearchAsync(string query, int pageSize, long pageIndex, string searchFrom = null)
        {
            // your custom search implementation starts here
            Dictionary<int, string> favouriteThings = new Dictionary<int, string>
            {
                { 1, "Raindrops on Roses" },
                { 2, "Whiskers on Kittens" },
                { 3, "Skys full of Stars" },
                { 4, "Warm Woolen Mittens" },
                { 5, "Cream coloured Unicorns" },
                { 6, "Schnitzel with Noodles" }
            };

            var searchResults = new List<SearchResultEntity>();
            
            var matchingItems = favouriteThings.Where(f => f.Value.StartsWith(query, true, System.Globalization.CultureInfo.CurrentCulture));

csharp
            foreach (var matchingItem in matchingItems)
            {
                // Making up the Id/Udi for this example! - these would normally be different for each search result.
                searchResults.Add(new SearchResultEntity()
                {
                    Id = 12345,
                    Alias = "favouriteThingItem",
                    Icon = "icon-favorite",
                    Key = new Guid("325746a0-ec1e-44e8-8f7b-6e7c4aab36d1"),
                    Name = matchingItem.Value,
                    ParentId = -1,
                    Path = "-1,12345",
                    Score = 1.0F,
                    Trashed = false,
                    Udi = Udi.Create("document", new Guid("325746a0-ec1e-44e8-8f7b-6e7c4aab36d1"))
                });
            }
            // Set number of search results found
            var totalFound = matchingItems.Count();
            // Return your results
            return new EntitySearchResults(searchResults, totalFound);
        }
    }
}