One way I've done is to wrap several (5-7) thin wires together with tape, winding downwards to make the trunk, leaving an inch or two exposed at the top. Cut the wires to different lengths (shorter ones are new growth).
Get some thin green tissue or rice paper and cut out several ovals that are the same length as the exposed wires. Then, using a fine scissors or sharp X-acto, cut a lot of angled lines in the ovals starting at one end and continuing to the next end. Leave a line of solid tissue down the middle lengthwise: that gets cemented to the wires. Once the leaves are cut, bend the exposed wires into drooping palm leaves, and then cement the cut tissues to the wires.
Paint the tape that is wrapped around the bottom wires brown and wash with black. Bend slightly into the curve you want, and then mount on your diorama base.
I know it is tough to follow without diagrams and pics, but I tried to be as concise as possible.
Hope this Helps.