$"\\begin{document}\n\\begin{tikzpicture}[\n every node/.style={inner sep=0.25em},\n edge from parent/.style={draw},\n level distance=3em,\n level 1/.style={sibling distance=15em},\n level 2/.style={sibling distance=2.5em},\n level 3/.style={sibling distance=2.5em},\n font=\\Large\n]\n\n\\node {S}\n child { node {B}\n child { node {a} }\n child[missing]\n child[missing]\n child { node {S}\n child { node {A}\n child { node {a} }\n child { node {S}\n child { node {b}\n \n }\n\n }\n child { node {b} }\n child { node {S}\n child { node {b}\n \n }\n\n }\n }\n child[missing]\n\n }\n \n \n };\n\n\\node[xshift=20em] {S}\n child { node {A} \n\t child {node {a}}\n\t child {node {S} child {node {B} child {node {a}} child {node {S} child { node {b}}} }}\n\t child {node {b}}\n\t child {node {S} child {node {b}}}\n \n };\n\n\\end{tikzpicture}\n\\end{document}"$