"optitrack motive" to ue4. how to create root bone

hello UE4 com…

i have *.fbx file with two skeletons and animation that was created/recorded with “Optitrack motive”
i cannot import this file directly to ue4 because those skeletons dont have the root bone.

i renamed one of the parent bones to :root, but without any luck
then i made simple skeleton in blender in the same scene with root bone and managed to import other skeletons and animations, but its not working properly.

my question:
how can i export one of skeletons with root bone as parent to all other bone structures?

i guess this is more blender question, but maybe someone have some good advice how can i import this fbx file in ue4 with skeletons and animations.

best

k/bit

problem solved

i just added mesh to skeleton(just cube) and named the whole skeleton as “root”
and it exported/imported just fine