Lara,
I don't know where to find a tutorial, but I'd be glad to tell you how I make trees....like this one:
You need to have several stringers, a striped one in green and black (or whatever you want your leaves to look like), a trunk one, so it looks good to be striped in shades of gray or brown...you can also throw some SIS into it--that looks nice! I like these stringers to be cased in transparent...it makes them easier to manipulate and more heat resistant.
Also you need rods in pea green, sky blue, green blend frit, colored blend frit, silver pink (optional)
I make a base bead, usually a barrel or bicone shape...1/2 blue and 1/2 green...then I roll it in white enamel...then I roll the bottom in a blend of green frit (GG mountain fern is what I use), I melt it in and then I roll the bottom half in some colored frit (Val COx Cherry Blossom is what I use). I melt that in...THEN I add splotches of silver pink in the sky...you can use white or whatever, but I love the look of the silver pink.
Then I press the base bead (this makes it easier for applying a tree)...I take my "trunk stringer" and in a downward motion I draw a line from about midway where I want my tree...I trail this down as one root...then I do it again...usually three times until I have the trunk as thick as I like it. Then I go to the top and add branches...just like I did the roots, just the opposite directs...sprawl them out across the bead. Last of all make "dots" in the green stringer all around the branches...
You need to make sure after applying the trunk that you kind of press it down a little so it doesn't pop off...if it does...don't worry, just add it again...if anything when that happens it adds a little interest. Also tamp the leaves down so the bond well with the base....
I wish I could do this with pictures...I will see if I can get DH to take pictures.
Oh, and if you want to do a palm tree...
You can make it in a very similar way....you use a twisted stringer and start at the bottom of the trunk and work upward...lay down the fronds in green and then rake them to make them look more realistic.