Data Abstraction?

[Matus]

Recently I finished a Binary Tree program. Though finished, my teacher's comments were "you did not abstract your data seperately" so here i am, i have an idea of what is meant but id like for some explanation better.

Ok so i have a structure like this:

typedef struct mystruct{
     int data;
     char charater;
     float dat;
    }MYSTRUCT;

so far what iv understood is that id have a separate struct like to manipulate the data, anyhow I'm just here for further advice, or if anyone can link me up to examples which shows this concept, I'd prefer examples if there are, i tried google but couldnt find any close to the concept, maybe its just me:

typedef  struct data{
       MYSTRUCT *data;
       struct data *right;
       struct data *left;
}DATA;

DATA *DataPtr;

Thanks