How to prevent from overlapping nodes in tikz

Question

I have created a tree-like structure using tikz package. The problem I faced is that the nodes haven't got enough distance from each other and I want to avoid giving the static distance. How can I handle that? Is there any way that it would work automatically?

\begin{figure}[h!]          
    \centering
    \begin{tikzpicture}[ scale=.6,
    every node/.style = { shape=circle,
        draw, align=center}]]
    \node {۱}
    child { 
        node {۲} 
        child {
            node {5}
            child {
                node {8}
            }
            child {
                node{9}
                child {
                    node{10}
                }
                child{
                    node{11}
                }
            }
        }
        child {
            node{6}
            child {
                node{12}
            }
            child{
                node{13}
                child {
                    node{14}
                }
                child {
                    node{15}
                }
            }
        }
        child {
            node{7}
        }
    }
    child { 
        node{۳} 
    }
    child { 
        node{۴} 
    }
    ;
    \end{tikzpicture}
    \caption{some caption.}
\end{figure}

in the following image you can see the overlapping of nodes:

Answer 1

Welcome! If you want to avoid this problem, consider switching to forest.

\documentclass{article}
\usepackage[edges]{forest}
\begin{document}
\begin{forest}
for tree={circle,draw,minimum size=2em}
[1
 [2
  [5
   [8]
   [9]
  ]
  [6
   [10
    [12]
    [13]
   ]
   [11
    [14]
    [15]
   ]
  ]
  [7]
 ]
 [3]
 [4]
]
\end{forest}
\end{document}

ADDENDUM: Is this what you are asking in the comments?

\documentclass{article}
\usepackage[edges]{forest}
\begin{document}
\begin{forest}
for tree={circle,draw,minimum size=2em}
[1,alias=first
 [2,alias=second
  [5,alias=third
   [8,alias=fourth]
   [9]
  ]
  [6
   [10
    [12,alias=fifth]
    [13]
   ]
   [11
    [14]
    [15]
   ]
  ]
  [7]
 ]
 [3]
 [4]
]
\path ([xshift=-1em]current bounding box.west) coordinate (aux)
 foreach \X in {first,second,third,fourth,fifth}
 {(\X-|aux) node[left]{\X}};
\end{forest}
\end{document}