SPI FLUSTERED BY ATC INSTRUCTIONS CLIPS TOP OF TREE ON APCH.

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I LEFT THE FLT SCHOOL TO PRACTICE SOLO TOUCH-AND-GO LNDGS AT BHM ARPT. I TOOK OFF ON RWY 23 AND WAS TOLD TO MAKE A R HAND TURN TO ENTER THE DOWNWIND LEG FOR RWY 18. I DID 1 TOUCH-AND-GO TO RWY 18. WHILE I WAS ON MY DOWNWIND LEG THE TWR TOLD ME TO 'TIGHTEN IT UP.' I TURNED BACK TOWARD THE ARPT TO TIGHTEN IT UP FOR THEM AND DID ANOTHER TOUCH- AND-GO. ON MY XWIND LEG THE TWR ASKED ME IF I UNDERSTOOD WHAT THEY MEANT BY 'TIGHTEN IT UP.' I SAID THAT I DID THEY THEN SAID 'RWY 18; CLRED TO LAND.' THIS STRESSED ME OUT BECAUSE THEY USUALLY CLRED ME FOR THE OPTION OR A TOUCH-AND-GO. I THOUGHT THAT THEY WERE NOT GOING TO LET ME DO ANY MORE TOUCH-AND-GO LNDGS BECAUSE I HAD DONE SOMETHING WRONG. WHILE I WAS ON FINAL APCH TO RWY 18 THEY SAID 'CLRED TO LAND ON RWY 23 AND AFTER LNDG GND CTL WILL GIVE YOU A TELEPHONE NUMBER TO CALL THE TWR SUPVR.' RWY 23 IS THE RWY THAT IS THE MOST CONVENIENT TO THE FLYING SCHOOL RAMP SO I DIDN'T KNOW WHY THEY WERE BRINGING ME IN. WHILE I WAS STILL ON FINAL FOR RWY 18; I NOTICED THAT I WAS GETTING LOW AND PWRED UP. I THEN HEARD A NOISE THAT I DIDN'T LIKE. I COULDN'T SEE OVER THE NOSE OF THE AIRPLANE TO TELL WHAT HAD HAPPENED. I GAINED SOME ALT AND MADE A L TURN TO SET UP FOR AN APCH FOR RWY 23; LANDED AND TAXIED TO THE RAMP. THE NEXT DAY I LEARNED FROM THE CHIEF FLT INSTRUCTOR AT THE FLT SCHOOL THAT I HAD BRUSHED THE TOP OF A TREE. CONTRIBUTING FACTORS WERE LNDG ON AN UNFAMILIAR RWY WITH HIGH TERRAIN ON THE FINAL APCH WITH A DISPLACED THRESHOLD THAT I HAD NEVER LANDED ON BEFORE AND THE STRESS OF WONDERING WHY THE TWR WAS SENDING ME BACK TO THE FLT SCHOOL. I SHOULD HAVE FLOWN MY AIRPLANE FIRST AND REMEMBERED THE OLD SAYING 'AVIATE; NAV; AND COM.'