Smoothing intersected bezier curves

Hello,
I have found some blender 2.4 tutorial about making trees. The problem is how to make that nice fill between duplicated curves, just like on the picture: http://wiki.blender.org/uploads/1/13/Tree_curve_base.png. I’ve been trying to configure somehow a bezier curve settings in properties panel and results are still like on left picture. Does anyone know what should I do?

Why do you think that is done with Bezier curves? No T-junctions are allowed in Beziers - anywhere AFAIK - and Blender’s NURBS implementation does not allow them yet (fingers X’d). Most likely done with meshes converted from curve objects before joining.

This effect is part of this tutorial: http://wiki.blender.org/index.php/Extensions:2.4/Py/Scripts/Wizards/TreeFromCurves#Basic_Shape. It looks like it’s made automatically using early version of sapling plugin.